- added a way to terminate QThreads safely by waiting; should be much safer
- made sure that the ArgsThread class receive the signal to stop
- made sure that on application shutdown, all workers will quit before the actual exit
- fixed the issue with factory_defaults being saved every time the app start
- fixed the preferences not being saved to a file when the Save button is pressed in Edit -> Preferences
- fixed and updated the Transform Tools in the Editors
