Add a new class ScanController which replaces the old ScanLib.

The new class takes care of scanning, the initial database setup, and complete collection scan, all moved to a separate thread.

This brings:
- progress info for the schema updating
- scanning is moved from the kioslave into the main process, which allows much better control (and some signals from the CollectionScanner in the future)
- all separated in its own thread, while the initial methods wait in an event loop for the process to finish.
I prefer this to processEvents().