Unify Database Interfaces into standard format, cleanup unused code

[wfehrnstrom]

There are a number of development efforts over the years that either were left half finished, or could not be accomplished for technical or goal related reasons. There have also been some changes related to the events API that have changed our event collection. So the goals are:

1. Get rid of all services that are a.) not being used by our production backend, AND b.) have no immediate use case associated with them
2. Get rid of database elements that are not being used in mlab where we store our database events
3. Unify as much as possible the code for handling events where appropriate, and where the code cannot be unified, standardize both the terminology used to reason about event collection and processing, and the interfaces on the functions used to collect and process events from disparate sources. This way, we lay the foundation for a potential total uniform handling of disparate sources in the future. Even if not, the immediate goal here is that we reduce cognitive load on ourselves as the backend developers.

Here are some immediate candidates for removal:
-user login related code
-all database event code that is not used for events_facebook_processed_collection, events_current_processed_collection and events_eventbrite_collection
-any ML code that is not used

Then, we need to do the slightly harder job of migrating events_eventbrite_collection functionality into events_current_processed_collection and finally, renaming all of events_current_processed_collection into events_eventbrite_collection.

Finally, as we remove these elements, we should document what features we removed, what files we deleted in removing the features. This is so that in the future, if any of the removed features might get brought back, that process can occur as seamlessly as possible.

Once all these objectives are satisfied, this issue is fixed.