Major Stability Improvements

Lots of stability improvements to address some long standing frustrating random crashes and freezes, the app is now much more stable overall. Fixd eoccasional freeze on startup and opening files. Fixed crash switching views, Fixed crash editing image units. Better handling of threading in general.

Changes to Outputs

Layers can now use processors as an overlay. Overlays are mixed with the main mapping layer processor using the alpha channel of the overlay.

Other fixes

QC Compositions work again, previous couple of updates caused glitching and slow playback, this is now fixed and qc renderes nice and smooth again