Rc2.1

C++ changes:
 - added runtime checks to addFactor
 - changed OPENGM_ASSERT . If OPENGM_DEBUG is defined all asserts will be checked even in Release mode 
 ( we need this to have OPENGM_ASSERTS in  unit-tests  in Release-mode)
 - ReducedInference Added a default value to Parameter in constructor  (pls add this for all solvers you implement next time)

Python changes:
- a lot... ( see commit messages)