user-accounts: Add an explanation of what enterprise login

https://bugzilla.gnome.org/show_bug.cgi?id=702478
user-accounts: Info message when we are offline

https://bugzilla.gnome.org/show_bug.cgi?id=702477
user-accounts: remove spinner from the password dialog

https://bugzilla.gnome.org/show_bug.cgi?id=702480