Improve repaint functions

Improve repaint functions

It is sometimes useful to be able to have better control on when a
repaint function is called. Currently, all repaint functions are called
prior to the stages update phase of the frame processing.

We can introduce flags to represent the point in the frame update
process in which we wish Clutter called the repaint function.

As a bonus, we can also add a flag that causes adding a repaint function
to spin the master clock.