[Android] Add support for external audio effect

[Alexandre Janniaux]

These patches add the support of Android API for writing external audio effect application like equalizers.
It needs the patch on libVLC to be able to pass audio session id as a command line parameter, otherwise the libVLC will fail to load as the parameter won't exist.
Currently, both external equalizers and vlc's internal equalizer would be in use at the same time if the user has one. It shouldn't be harmful as the vlc's one is disabled by default. Maybe the equalizer button should try to open an external equalizer and if none is found, open vlc's one.

This could also be used to detect other equalizer and disable vlc's one according to preferences (automatic, forced external, forced internal) in that case.

In the future, it might be a good idea to be able to set this id directly from the media.GIT: [PATCH 1/2] Generate audio session id in VLCOptions for libVLC

It includes the following patches:

+ [PATCH 1/2] Generate audio session id in VLCOptions for libVLC
+ [PATCH 2/2] PlaybackService: send EFFECT_CONTROL_SESSION on media