* many changes:

  - merge separate account_ and server_account functions into one
  - fixed signals when changes take place in the backend (modest conf)
  - removed internal cache of account names, but always use modest-conf
  - cleaned up 'check_change'
  - implemented enabling/disabling of accounts, and signals understand this,
    as well as the 'search' function
  - simplified a lot of code, refactoring, cosmetics

pmo-trunk-r359