This is only the bare minimum to make everything under panels/common
build. Since these widgets are used by the main window, port them
first.
CcTimeEntry was particularly hard to port. That's because GtkEntry
is a final class now. Overall, though, I'm happy with how it turned
out to be - much cleaner, less code, more obvious.
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 big set of changes that aim to set a consistent
authentication method accross Settings panels.
See #685, #556, and #771
