make addon work on linux / with ofGstVideoPlayer

[evsc]

Instantiates ofGstVideoPlayer() instead of ofQuickTimePlayer(), doesn't define USE_QUICKTIME_7 and USE_JACK_AUDIO if your with a gstreamer player.

The rest is: commented out assert() calls because they didn't work for me. And i got rid of some small warnings (unsigned int compare, switch without default).