Moving a few base class throttles and fields from the events app up
one level so that they can be used elsewhere.

Moved events.api and superevents.api into the new api app.
We want to have a versioned API, so these are now in
api.v1.events and api.v1.superevents, respectively. Part of this
change is that we require a custom reverse function (api_reverse)
for handling versioning. Much of the required code changes for this
migration include converting reverses to use this function and
changing relative imports appropriately.