GLMixer Code

Added new texture masks (pixel lines and grids, gabor patches).

compilation compatibility for libavcodec < 56

Changed behavior of property browser on change of source: avoid
reconstructing the whole property tree which was slowing down rendering.

Fixed lintian warning package-contains-timestamped-gzip in cpack

Bug Fix in installation procedure. Spell check in README.

Bug Fix: removing remaining tests in glmixer source edit

Simplified Media Source and Video File implementation. Removed option
'Seek dirty frames' which was useless and buggy.

Finalize the re-implementation of VideoFile without the parsing thread.
Fixed the seek mechanism.

Removing Parsing thread in VideoFile: I surrender in finding how to
avoid memory leak in the packet queue... This new implementation reads
packet and decodes picture in the same thread. Memory leak seems fixed
(althouth i am not fully satisfied). NOT STABLE FOR SEEKING.

Bug Fix: reading info on rendering size (width, height) from
RenderingManager was dependent on initialization of fbo, causing error
when fbo was reset. (this also fix the reading of SVG source).