Lots of updates:
- The lesson will automatically add an exercise behind a slide if that slide has a defined Smyth ref.
- Implemented a super simple case for identifying the person of a verb. Will generalize.
- Most importantly, direct select exercise works async, so loading a lesson is quite fast.
- Changed loading lesson content from an AJAX request into a RequireJS text include.
- Renamed mapper.json to smyth.json, so it's clearer what's inside it.