Squashed 'lib/QPersistence/' content from commit 9ecf403

git-subtree-dir: lib/QPersistence
git-subtree-split: 9ecf403f99edda0144ed5bacd1e7dd5e01b5313d
Merge commit '89c1782f7ec6c5c1c0fa688e7926a3960bf8e8d5' as 'lib/QPersistence'
Added the new model and started removing things, that were necessary for the conversion of old databases.
Improved the performance the player<->round relations of Qp::readAll in general