Feature/issue 103 initialize state

#### Summary

The initialization code is now calling the initialization routines in stan's src/common/initialize_state.hpp

### Details

- added a context_factory in rlist_ref_var_context_factory.hpp
- cpp tests are now runable again; added a (complicated) test
- RStan unit tests had to change to find the strings from src/common/initialize. Behavior is the same, just the error message is different.