Improved fullscreen support on OS X (close #343)

No hard resolution switch is done. Instead a view of the requested
size is displayed in the center of the main screen (letter boxing).

Running a stress test showed that the performance were equal
to a hard switch without the inconvenience of resizing the
user's apps. This also follows the guidelines defined by Apple:

> Avoid changing the display resolution from that chosen by the user.

source:
https://developer.apple.com/library/mac/documentation/graphicsimaging/Conceptual/OpenGL-MacProgGuide/opengl_fullscreen/opengl_cgl.html
Add support for retina displays (close #353)

Based on PR #388 by Michael Bradshaw

Convert size to match the size requested by the user.
Replaced some deprecated functions on OS X

NSWindow convertBaseToScreen: -> convertRectToScreen:
NSView   convertPointToBase:  -> convertPointToBacking:
Fixed mouse tracking in fullscreen on OS X