Fixed all NHibernate unit tests by implementing missing persistency
methods, tables, columns and fixing bugs in the existing implementation.
Two minor changes to classes outside NHibernate module: Added Scene
instantiation for SceneObjectGroup in OpenSim.Data.Tests.BasicRegionTest
as this was required by the NHibernate persistency. In the process added
also mock constructor to Scene which only populates RegionInfo in the scene
which is used by ScenePart.RegionUUID. NHibernate module is still in
experimental state and has not been tested at opensim region or ugaim runtime
configuration. Adding unit tests to build is not yet advisable nor using
NHibernate module in any production setup.
