We need to disconnect the frame clock when we unrealize (at which
point the old clock is still alive) not in destroy(). Since there
is no common unrealize for containers, trigger this from GtkWidget.
Instead of using 1 global queue for both resizes and style validation,
use 2 queues. This makes the code a lot simpler and fixes a bug where we
could accidentally stop restylying for very delayed restyles.
