Update TODO.
Partially fix cell renderer speed issues with GTK+ 3.6 and later.

Since GTK+ 3.6, the notify::text signal seems to get emitted insanely
often even if text hasn't changed at all. Let's try to keep our callback
as fast as possible using 1000 value memoization mapping text to markup.
Update TODO.
Use a signal to relay state changes.
Merge ../gaupol into gst

Conflicts:
	TODO