MacGui: Set the hud control panels origin based on the size of the actual preview...

MacGui: Set the hud control panels origin based on the size of the actual preview window anchored at the bottom instead of setting it at the middle of the window.
- Should not block the actual preview as much.
- Move the origin setting code from -SetTitle into -displayPreview so that it is recalculated any time a new preview is generated, which includes changing encode size.

git-svn-id: svn://localhost/HandBrake/trunk@3349 b64f7644-9d1e-0410-96f1-a4d463321fa5