Screen/PsychImaging: Add support for display rotation via panelfitter.

Extend the Screen() panelfitter to handle rotation of the framebuffer:
Imaging pipelines identity blitter now also accepts optional paramters
for rotation of the final image by some 'Rotation:%f' angle around a
'RotCenter:%f:%f' cx,cy center and applies it if a non-zero angle is
specified.

The panelfitter code takes advantage of this rotation. It adds angle,
cx and cy as new optional parameters for the Screen('PanelFitter')
parameter vector to set those params. If a non-zero angle is requested,
the fallback path with texture blitting via kPsychIdentityBlitChain is
used, instead of the faster glFramebufferBlit code, which is incapable
of rotations.

PsychImaging has new high-level setup code for rotation during panel
fitting, as exposed in PsychImaging('UsePanelFitter') via a new
optional 'angle' parameter, and for convenience, via a new
PsychImaging('UseDisplayRotation') function for display rotation only.
The current setup code has bugs or limitations: It only handles either
scaling/fitting or rotation well, and usually also only rotation by 90
degree increments. Iow. it handles the most common use case right, but
fails in various ways for more exotic or complex demands.

-> Screen for 64-Bit Matlab on OSX rebuilt and tested.
-> A new demo PanelFitterDemo.m demonstrates use of the panelfitter for
display rotation, scaling and panel fitting.