Refactor the overlapping element code to remove the time consuming recursion. Leads to huge speed ups in drawing of overlapping elements. Move to the Row class where it could be used elsewhere if needed.

Other minor clean ups.
Fix row cutting off the top when it is partially scrolled off.
Fix the gray image painting while the cached image is regenerated. Use a stretched version of the cached image until it can be re-rendered.

Try to suppress the cancellation exception.
Detect individual row resize events and re-render the elements.
Merge remote-tracking branch 'remotes/jeffu231/TimelineImprovements'
Fix individual element rendering for move/edit.
Contain the row height to the grid height.
Suppress additional rendering requests while clearing the queue.
If we reach the row height cap and height did not change, don't re-render them.
Invalidate visible effects as they are rendered, so they can be seen sooner.
Contain the unnecessary OperationCanceledException.
Merge pull request #25 from sall/master

Merge from sall/vixen