Mostly rewrite the VideoDisplay sizing logic

Fixes layout errors after maximizing when the window previously wasn't
big enough to fit the video and an infinite loop caused by wxGTK not
updating the window size immediately.

Makes it so that the bottom video toolbar is not pushed offscreen by
high video zoom. This is not always desirable, but should be an
improvement in most cases.

Closes #1409.

Originally committed to SVN as r6926.