Deprecate ImapAccess::password on behalf of the PasswordWatcher

Also fix the PluginManager so that parent goes first, as in the rest of Qt.

The Harmattan UI gets adapted to always ask for the password.
Disable QtKeychain on Harmattan

There's no QtKeychain on Harmattan anyway, so don't let our host environment
confuse stuff. It won't work, it's a runtime library after all.
Add password plugins

Merge branch 'pali-plugins-wip'

Conflicts:
	src/Imap/Model/ImapAccess.h

REVIEW: 117568