Big refactor: Replace Palapeli::LibraryModel by the three classes Palapeli::Collection, Palapeli::ListCollection and Palapeli::LibraryCollection. 
Import/export and deletion are dysfunctional currently, but the internal design is much better, because we're mostly passing around QModelIndexes 
now, and the identifiers are really universally unique.

svn path=/trunk/playground/games/palapeli/; revision=1034075