Add Ability to Re-categorize All Events in a Category

[gmcquillan]

Some categories are mostly duplicate. To fix this:

1. delete the category reference in the '''categories''' key.
2. push each event from that data_<cat_id> into input.
3. delete data_<cat_id> when it's empty.

[gmcquillan]

This is pretty much done on the backend, I think. We just need to be able to expose it via the UI somehow.