Refactor tags controller to query MongoDB
Refactor tweets controller to query from MongoDB

It is worth noting that I did not port over the :otd or :ntd
parameter parsing because it appears that those code paths are
not used anywhere.
UI updates for new api/mongo response
Remove remaining vestiges of MySQL

With the exception of the migration script, of course.
Add tweet aggregation for metrics usage
Refactor admin panel to use Mongo aggregation collection
Refactor suggestions to use Mongo