This patch includes a lot of work to refactor and reorganize the

This patch includes a lot of work to refactor and reorganize the
account settings dialogs. The main improvement is the implementation
of ModestAccountSettings and ModestServerAccountSettings. These
classes represent the settings of accounts and server accounts in
memory, avoiding storage in ModestConf for temporal or non persistent
account settings.

* src/modest-protocol-info.[ch]:
        * New method modest_protocol_info_get_connection_protocol, that
          obtains a ModestConnectionProtocol from a string.
* src/modest-server-account-settings.[ch]:
        * New class, that represents server settings (common for
          store and transport server settings. It's only a memory
          storage. Persistence is managed in ModestAccountMgr.
* src/modest-account-settings.[ch]:
        * New class, that represents an account. It contains two
          ModestServerStoreSettings for store and transport accounts
          associated with the account. It represents all the common
          account information (display name, user fullname, email
          address, etc).
* src/modest-account-mgr-helpers.[ch]:
        * Added internal method null_means_empty for avoiding setting
          NULL to values we shouldn't put NULL.
        * (modest_account_mgr_get_store_protocol): use the new
          settings api.
        * (get_secure_auth_for_conf_string): removed, as it's also
          in ModestProtocolInfo. Also use
          modest_protocol_info_get_auth_protocol_name instead of
          the big if.
        * (get_security_for_conf_string): removed, as it's also in
          ModestProtocolInfo. Also removed if.
        * Replaced modest_account_mgr_get_server_account_data with
          modest_account_mgr_load_server_settings. The method creates
          an instance of ModestServerAccountSettings from a ModestConf
          account.
        * Removed free method for server account data.
        * Added method modest_account_mgr_save_server_settings. It
          stores a ModestServerAccountSettings in ModestConf.
        * Replaced modest_account_mgr_get_account_data with
          modest_account_mgr_load_account_settings. This fills a
          ModestAccountSettings instance with information, and
          also obtains the store and transport server settings. Also
          removed old ModestAccountData and ModestServerAccountData
          structs.
        * New method modest_account_mgr_save_account_settings, that
          saves an account to ModestConf. It's more intended for
	  updating an existing accoung.
        * Methods get_retrieve_type_name and get_retrieve_type, to
	  convert from string representation of retrieve types into
	  modest ModestAccountRetrieveType and viceversa.
* src/modest-account-mgr.[ch]:
        * New (modest_account_mgr_add_account_from_settings): creates
          a new account in ModestConf, and emits the signal to register
          it in the list of available accounts.
        * Usage of ModestAccountRetrieveType instead of conf strings.
        * Use ModestAccountSettings and ModestServerAccountSettings
          instead of deprecated ModestAccountData and
          ModestServerAccountData.
* src/modest-tny-account.c:
        * Use ModestAccountSettings and ModestServerAccountSettings.
* src/modest-tny-account-store.c:
        * Use ModestAccountSettings.
* src/modest-mail-operation.c:
        * Use ModestAccountRetrieveType instead of strings.
* src/modest-widget-memory.c:
        * Use ModestAccountSettings.
* src/widgets/modest-retrieve-combo-box.[ch]:
        * Use ModestAccountRetrieveType instead of strings.
* src/widgets/modest-account-view.c:
        * Use ModestServerAccountSettings and ModestAccountSettings.
* src/widgets/modest-header-view.c:
        * Small change, if model is NULL, expose returns silently.
* src/modest-ui-actions.c:
        * Use ModestAccountSettings api.
        * Make some specific maemo code be now usable again also
          in gnome port.
* src/maemo/modest-connection-specific-smtp-window.c:
        * User ModestServerAccountSettings api.
* src/maemo/easysetup/modest-easysetup-wizard.[ch]:
        * Big work here to adapt to ModestAccountSettings. As a benefit,
          now we use it to pass the settings to
ModestAccountSettingsDialog
          (advanced settings). We only save to the account manager on
          finishing and approving changes.
        * Moved code to create the account to ModestAccountMgr, and
	  added code to fill the ModestAccountSettings.
* src/maemo/easysetup/modest-easysetup-provider-combo-box.c:
        * New method to set the provider to others.
* src/maemo/modest-account-view-window.c:
        * Use ModestAccountSettings.
* src/maemo/modest-account-settings-dialog.c:
        * Use ModestAccountSettings.
        * Move storage and fetch code from ModestConf to account
	  manager.
        * Added code to fill and retrieve information in
	  ModestAccountSettings and ModestServerAccountSettings.
        * Now it works with ModestAccountSettings, instead of storing
	  directly to ModestConf.
* src/maemo/modest-main-window.c:
        * Use ModestAccountSettings for management of accounts menu
          options.
* src/maemo/modest-connection-specific-smtp-edit-window.c:
        * Use ModestServerAccountSettings.
* src/modes-platform.h, src/maemo/modest-plaform.c,
  src/gnome/modest-platform.c:
        * Provide methods to retrieve an instance of the account
          settings dialog and the account settings wizard.
        * Provide valid implementation of some dialogs in gnome port.

And some work for splitting modest-maemo-utils in modest-utils (for
common usable methods) and modest-maemo-utils (specific maemo platform):
* src/modest-utils.[ch]:
        * New set of methods, now available for all modest platforms.
        * Reworked many other objects, to use this split.
* src/maemo/modest-maemo-utils.[ch]:
        * Moved a lot of methods to modest-utils.

pmo-trunk-r3846