Start using media library

Forgot this file

* Fix a memory leak / crasher

* Start putting together all interface strings (Refs:#703)

* Fix a nasty playlist crash

 * Add atrack, vtrack and strack commands. Those can be use to display/change audio, video and subtitle tracks.
 * Fix compile warning in enqueue command.

  This should help identify the producing encoder and fix some issues with codec specific problems

put mono audio in both (left/right) channels. For some reason AOUT_CHAN_CENTER doesn't work. Somebody explain this to me, please.

* Does nothing useful at the moment (only useless device probing)
* The purpose would be to make an access-demux and an access sub-module reusing part of the code
* Access to a webcam or an analog card without an encoder (bt878) would help the development