Debug code causes exceptions when destination type is other than CommunityDestination.
More debug code.
Removed unused import.
Moving unittest code into tests directory.

debug.py and debugcommunity.py have been split into one file per class
and moved into tests/debugcommunity/.  Import statements have been
modified to reflect this change.

Other minor changes:
- DebugNode now takes community as a parameter instead of calling
  set_community
- Method names in DebugNode have been modified from create_..._message
  into create_...
- Documentation has been added.
Merge pull request #17 from boudewijn-tribler/debugcleanup

Moving unittest code into tests directory.