Added support for opening the addressbook from the main window

Added support for opening the addressbook from the main window
through menu (fixes bug NB#57590):
* src/modest-platform.h:
        * Added method to show the addressbook UI.
* src/modest-ui-actions.[ch]:
        * Add action handler to open the addressbook UI.
* src/maemo/modest-main-window-ui.h:
        * Add callback handler to show addressbook from main
          window menu.
* src/maemo/modest-platform.c:
        * Added implementation to show the addressbook
          from modest using osso rpc.

pmo-trunk-r2113