GStreamer-1.4: Cleanups + bits of HDR support.

Cleanup dead code, beautify etc. Improve error handling a bit. Add
support for the Schroedinger codec ‘schroenc’ which can encode 16 bpc
YUV as Dirac video stream and store in a qtmux or matroskamux Quicktime
or Matroska container at up to 16 bpc. Add new pixelFormats 9 and 10 to
playback engine to allow decoding 16 bit grayscale and 16 bpc ARGB64 to
16 bpc luminance or RGBA float textures.

So far the theory. In practice encoding seems to work with
Schroedinger. However trying to playback such high bit depth video
crashes the app by triggering an assertion + abort() inside
libschroedinger. Same happens with GStreamer command line tools, so not
a PTB bug. I don’t have any other suitable video players for testing
the high bit depth stream. VLC decodes it without problems, but doesn’t
display anything.

Anyway, the groundwork is laid out.

-> Screen for 64-Bit Octave on OSX rebuilt and tested.
-> ImagingStereoDemo.m contains a new example line for Schroedinger
encoding.