Draft: ProgressBar: Get rid of custom timer/animation hack for indeterminate state

This is obviously a work-in-progress proof-of-concept, but given an idea what is needed to implement it properly. Basically we'd want to connect and disconnect refreshes only when the control is a progress bar and (minimum == 0 && maximum == 0) i.e. when it's in indeterminate state.

This solution is highly inefficient (requesting a repaint on every frame for every control). But it works as expected.