It misses some frames, it also crash, but it's good enough for now.
I'll debug it as it goes.

It just lacks RenderPreviewWidget to query only one frame at a time.

This reverts commit 68f40c44.

This reverts commit 295c52c5.

(coming soon :p )

Added a basic media player pool

It broked the uuid value on windows.

The clip QMap has been thread safed for the occasion (and to resolve a
few bugs)
Though, it seems to miss some events sometime (without crashing,
changing position is enough to restore the render preview)

Removed some debug texts

There's still some problems on the workflow rendering if we specify a
length.

Now media isn't cloned from on vlcmedia to another, since they share
options. A new one is creater from scratch.