[opf] fixed lazy loading initialization
[tests] fixed class registry of invoice model
[tests] fixed scenario
[opf] splitting the select generator into base/complementary/collection
[opf] doc of friend class assignment
[core] including a protected property to the model.fmetadatamap attribute
[tests] some inheritance tests
[opf] fixed AV if an exception raises before pid is assigned
[opf] proper classref naming; fix doc
[opf] multi map select implementation