Implement versioned resource storage

That patch implements the following:

1. Reloading of the dirty presets
2. Fixes marking of presets as dirty when "Save temporary tweaks" is both on and off
3. Implements proper versioning for Bundle, Folder and Memory storages.
4. Implements syncing of the database with the content of physical storage (on Krita restart, not on the fly, which is out of scope). Basically, you should now be able to add/remove files to the _modified folder, restart Krita and Krita should detect new and/or deleted files.