Added delete functionality to the db and stubdb

Added tests for stub db. Still have 99.4% coverage or whatever it is
for the stub db.

No GUI functionality so it's hard to test the real db (I didn't want to
mess with the GUI)
Forgot to update puzzlemanager to delete puzzles

PuzzleManager now has delete puzzle functionality and is tested.
Merge pull request #24 from williamhc/delete-puzzles

Looks good to me.  Onto integration tests!