ProgressDialog doesn't have to worry about the platform anymore, now
MainWindow will determine what to do or whether to ignore certain progress
indicator functions.
Made various changes and fixes to the task system:
- Tasks are built around QtConcurrent rather than QThread. Reduces
code complexity significantly.
- Task error reporting is now streamlined in both TaskManager and
TaskDialog.
- Moved ProjectImport/Save/LoadManager to the app/task folder
itsmattkc