Fixed multi-threading issues with nodes. Still some fixes needed for EXRs
Merge branch 'workshop' of github.com:MrKepzie/Powiter_Core into workshop
Rows are now always computed at full res
Preview is now handled by the Reader class and not by the Read. Speeded-up tons the decoding buffer of the reader. Still issues with exr's.
Preview is now also computed in a separate thread and the row used by the preview are cached so it speeds-up the following requests for these rows.