Removing uneccessary code.

No point in using a QAbstractItemModel if GridView interprets the model as a
list, use QAbstractListModel. Defining a user role just for the name isn't
worth it.
Define images for tiles in QML.
Inform user of number of levels in collection.
Handle signals when going to previous level.
Show message when level is complete.
Rename variable to conform to coding style.
Level parser fix.