merged QpAbstractObejctListModel into QpObjectListModel
Added convenience methods to QpSortFilterProxyObjectModel
Removed idiot-methods from QpCache.
Fixed a major bug in DAO, where removing objects would lead to nullpointers in the list returned by readAll
Relations now clear themselves, when a nullpointer is passed to relate()
Merge commit '29ee6216e82ca8a8711c99ecbde2a9fbfd22cca9'

Conflicts:
	lib/QPersistence/src/cache.cpp
	lib/QPersistence/src/cache.h
	lib/QPersistence/src/dataaccessobject.cpp
	lib/QPersistence/src/objectlistmodel.cpp
	lib/QPersistence/src/objectlistmodel.h
	lib/QPersistence/src/relations.cpp
	lib/QPersistence/src/sortfilterproxyobjectmodel.h
	lib/QPersistence/src/sqldataaccessobjecthelper.cpp
	lib/QPersistence/src/sqldataaccessobjecthelper.h
	lib/QPersistence/tests/tst_cachetest.cpp
Merge commit '42b06c316f22540e07b1f62309d495372c5abe07'
removed qp to clean subtree
Squashed 'lib/QPersistence/' content from commit 42b06c3

git-subtree-dir: lib/QPersistence
git-subtree-split: 42b06c316f22540e07b1f62309d495372c5abe07
Merge commit 'c9e5ab6f354eaad4d20cd5111bc8e36dcdb99805' as 'lib/QPersistence'