Fix invite user invitation messages
MediaScanner refactoring & fixes
Moved scan start to the scan() method
MediaScannerDialog -> MediaScanner (still have to remove the WDialog inheritance)
Using shared_ptr for MediaScannerSteps
MediaScanner isn't a dialog anymore
Preparing Pandorica object for shared sessions refactoring
Refactoring inter-session callbacks
Using d_ptr for Pandorica too
Using internal path to browse media directories
Tidying up endSession method