Cleanup VideoMultiCameraCaptureDemo and VideoRecordingDemo.

Use 8 bpc capture by default in VideoMultiCameraCaptureDemo again.
Remove legacy Quicktime support from VideoRecordingDemo. Also clean
up help text a bit.
Screen: Add initial video recording support to dc1394 video capture.

Use the GStreamer movie writing functions internally to provide
video recording support for the libdc1394 based engine.

Should support same semantic/codec options and types as
movie writing and GStreamer video capture engine for
recording.

This also makes sure that returned uint16 memory buffers or
Matlab/Octave image matrices are left-shifted so the 16th bit
contains the MSB of the camera sensor data.

The same shift to align 16th bit == MSB is applied to data that
is sent to the video encoding.

Additionally change average pixel intensity calculation in both
dc1394 engine and GStreamer engine to always return normalized
intensity in the 0.0 - 1.0 range, so we get rid of all the
ambiguities around 8 bpc vs. 16 bpc vs. intermediate bcp value
range.

This commit also verifies correct working of the 16 bit signed
normalized texture creation fallback path if floating point
textures are not available.

What doesn't work yet is lossless encoding of video, or of
16 bpc video, as most codecs do not support 16 bpc or only
lossy compression. Attempts with lossless jpeg or png so
far failed. Encoding sometimes works, but decoding/playback
doesn't.

-> Screen for 64-Bit Octave on Linux rebuilt and tested.