Create event and revision services
Merge branch 'develop' into feature/log_events
Merge branch 'develop' into feature/log_events
Move migration file into extension location
Add basic page, widget, and CanJS model for Events listing
Update newly added columns to sensible defaults
Add person and revision to UI
Add modified_by relationship to ChangeTracked mixin
Include modified_by in findAll
Use eager_query instead of relationship option to load revisions
Enable alembic `current` command

* usage: python -m ggrc.migrate <module> current
* also fixed `args` indexes
Add `ReadOnlyResource` for `events` and `revisions`
Merge pull request #62 from reciprocity/feature/log_events

Feature/log events - includes migration
Merge remote-tracking branch 'origin/develop' into feature/contexts_service
Fix migration to reset all `context_id` to NULL

* required for foreign key constraint to be created
Rearrange inheritance order so eager_query works correctly

* otherwise there is a 'people' query for every object due to
  `modified_by` relationship