Add check for input purpose for gnome-shell password dialog

Resolves: rhbz#1061345 - ibus-table shows entered text in password fields
(See: https://bugzilla.redhat.com/show_bug.cgi?id=1061345)
Merge pull request #25 from mike-fabian/add-check-for-input-purpose-for-passwords

Add check for input purpose for gnome-shell password dialog