[common+ user-accounts] Introduce CcPermissionInfobar widget

The "CcPermissionInfobar" widget is a more descriptive way to communicate that some Settings panel needs authentication in order to perform certain actions.

This widget doesn't handle the permissions (as in GPermission) itself. It needs to be binded to an existing instance of GPermission, and it will react to the permission's state (show when the current user is not authorized, and hide when the user is authorized).

This is part of a set of changes that aim to set a consistent authentication method accross Settings panels.

See #685 (closed), #556 (closed), and #771 (closed)