This moves a couple of definitions to the common types header, and makes
sure that ClutterBehaviour subclasses include clutter-behaviour.h first,
so that their types can be fully expanded without necessarily have the
ClutterBehaviour header header included by their public headers. This is
the necessary prelude to have clutter-behaviour.[ch] moved to the
deprecated section.
The code that has been deprecated should live into its own directory,
both in the repository and when installed. This should make it clear
which functionality is actually maintained and which is not.
We start with an oldie: the frame source API.