Merge pull request #38 from ireynolds/message_effects

Added a model for communicating the effects of a message signal receiver.
Updated MessageEffect to use priority levels instead of a success boolean.
Replaced implementation of OperationBase to make use of MessageEffects. Updated naming conventions for stages. Existing operation implementations no longer work.
Replaced broken imports--tests now run.
Reorganized Parser rapidsms app.
Made messagelog app run before any of our code to put logger_msg field on the Message instance.
Moved simtest target into utils app, added test superclass that uses modified router from settings.
Moved OperationBase to utils.
Moved test code to utils, tests run only on subset of apps.
Isolated tests of OperationBase to only one mocked app.
Tests syntax stage of OperationBase.
Tests calling semantic subscribers.
Removed duplication between subscriber test classes.
Checks parse, semantics, and commit for multiple operations.
OperationBase test remembers all calls to commit and semantic signals.
Reasonably complete tests for OperationBase.
Better naming in OperationBase tests.
Added skeleton for a very simple documentation site.
Merge branch 'master' into user_models
updated regstration models and moved to registration app