Work to fix NB#84828.

Work to fix NB#84828.
* src/modest-ui-actions.c:
	* Dim the username in get password dialog _always_. We don't want to
	  allow to change the username from here, as we can cause hangs
	  because tny_account_set_user here is inside a lock.
* src/modest-tny-account-store.c:
	* Remove the call to set user as we never change the password from the
	  get_password dialog.
* src/maemo/modest-account-settings-dialog.c:
	* Allow to change the smtp username in account settings dialog.
* src/modest-window-mgr.c:
	* A minor issue with modality. If the window we're destroying is
	  on top, we remove the current_top reference, to prevent one warning.

pmo-diablo-r4459