Basic start for medias's metatags. They're stored in the media, and displayed in the media property dialog

Cleaned MetaDataManager/Worker code, removed renderWidget, avoiding to permanent warning.

This reverts commit b99c1c6e.
There's a blocker which needs to be fixed first.

Added LibVLCpp::MediaPlayer destructor, avoiding event crashes
Fixed potential memory leaks
Removed junk code, corrected minor typo

Pause can be toggled until every single ClipWorkflow of every single TrackWorkflow has been paused.

This reverts commit df19117a.

This reverts commit c076f2b7.

This reverts commit c277adec.

This reverts commit 27b832c3, reversing
changes made to c277adec.

Conflicts:
	src/Workflow/ClipWorkflow.cpp
	src/Workflow/MainWorkflow.cpp
	src/Workflow/TrackWorkflow.cpp
	src/renderer/WorkflowRenderer.cpp

This reverts commit e7b6d21a.

This reverts commit 37a0076e.

Pausing is now using a event stack

I finally renamed a method starting by m_, this was pissing me off for weeks :)
This solves the random crash due to letting Qt delete the main workflow. MainWorkflow is a QObject, but
it's not Qt's job to decide when to delete it, since it used by at least 2 widgets which are deleted in an
arbitrary order...

This fixes issue #30.

Performance are really improved, ie previewing is as fast as watching a video in VLC