VisibleEntity must be abstract, it does not make sense to initiate VisibleEntity alone.
Flag signalizing whether entity is registered or not, was added.
Import added.
Few entities are present in the game. Graphical map is generated from paths and castles.
Test libs added along with basic tests. If tests use objects that are linked to OpenGL content, dummy application has to be initiated ad these objects has to be created in OpenGL thread.