Selection media cell in Library

Conflicts:
	src/GUI/MainWindow.cpp
	src/GUI/ui/MainWindow.ui
	vlmc.pro

Bug fix: seg fault on selecting an new item when the previous was deleted.

This apparently solves every current problem, and since audio memory input isn't implemented in VLC yet : not a problem at the moment.

Conflicts:
	src/EffectsEngine/OutSlot.hpp
	src/GUI/MainWindow.cpp
	src/GUI/ui/MainWindow.ui
	src/LibVLCpp/VLCMedia.cpp
	src/Renderer/WorkflowRenderer.cpp
	src/Renderer/WorkflowRenderer.h
	src/Workflow/ClipWorkflow.cpp
	src/Workflow/ClipWorkflow.h
	src/Workflow/MainWorkflow.cpp
	src/Workflow/MainWorkflow.h
	src/Workflow/TrackWorkflow.cpp
	src/Workflow/TrackWorkflow.h
	vlmc.pro

Still not functionnal, I think something was lost in the merge...

Conflicts:
	src/GUI/ui/MainWindow.ui
	vlmc.pro

Add of a delete button on the media cell and an hightlight selection.

When a media is selected, preview widget shows the snapshot so the user is aware of which clip is going to be previewed.
Black background is now always shown, even when previewing.

Please update vlc to the newest version

Removing the ugly hack to make the QSharedDataPointer doesn't screw the memory, because it wasn't that

We finally discovered where was this fu****g memory corruption bug, thx to Chouquette, I want also thanks my mother, my father and "Bernardmy pony