ui/cocoa: Fix several full screen issues on Mac OS X

ui/cocoa: Fix several full screen issues on Mac OS X

This patch makes several changes:
- Minimizes distorted full screen display by respecting aspect
ratios.
- Makes full screen mode available on Mac OS 10.7 and higher.
- Allows user to decide if video should be stretched to fill the
screen, using a menu item called "Zoom To Fit".
- Hides the normalWindow so it won't show up in full screen mode.
- Allows user to exit full screen mode.

Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
[PMM: minor whitespace tweaks, remove incorrectly duplicated
 use of 'f' menu accelerator key]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>