returns true if unit has target

Changed getTarget() in Unit.cpp to return Unit() if no target found

Integrate all information from TechTreeImproved into the existing class
TechTree. Thus TechTreeImproved is deprecated and removed from the
Python-API.

CCUpgrade (sc2::UPGRADE_ID) does not contribute much and makes code
more difficult. Especially in Python, since it does not convert between
types implicitly.

This is a nice feature, but it took too long to force CMAKE into
outputting the binary into the correct directory.