GLMixer Code

Bugs fixed:
- new session badly triggers geometry view
- rendering manager not coming back to source drawing mode false
- layers view look at

Fixed bad implementation of aspect ratio reset functions
+ set the behavior of sources displacement in Layers view to get back in
place after moved.

remove fogotten debug

fixed bug tooltip mixing presets

Complete reimplementation of the Layers View :
- picking using FBO and depth map
- selection area (sub-classed)
- zoom best fit
+ coherent implementation for other View

Improved GUI glmixer
added butons to add date and list of sources in the bloc notes.

Bugs fixed:
- no effect on zoom action for RenderView
- stop / play of a video source paused: keep the pause state
- no reset of the video_current_pts time on start video file
- disable action 'delete' when no current source available
- restored shadow of frame in Geometry and Layers view
- improved layout of SessionSwitcherWidget

Improved rendering of the groups in mixing view

Fixed rendering bug in Mxing View (missing shadows) : generalized the
fix to all similar cases (reset the vertex array).

changed menu action 'toggle modifiable' to the check box action
'Unchangeable'