Ensure that the factory is initialized before using the account manager

GoaTelepathyProvider is not the only one who uses the account manager.
GoaTpAccountLinker uses it too. We should initialize the client
factory before using the linker so that we really have all required
account and connection features.

Fixes: https://bugzilla.gnome.org/708399
oauth2: Propagate the error if the dialog is dismissed during refresh

Fallout from a6ce50a8ab89242d7d25611c3828033e854a263d

Fixes: https://bugzilla.gnome.org/708832