Add combineReducers()

Additions:

• Add combineReducers() for combining Flambeau-style reducers.
• Dispatched actions now always have a type (of FLAMBEAU_ACTION_TYPE).

Breaking changes:

• getConsensus() now accepts getStates() instead of states.
• Built-in store class is now exported at flambeau/Store – this might be removed outright down the line.
• Removed SimpleGraphController.