Replace "events" table with "events_for_migration"

In 9.5 we introduced a new temporary table called "events_for_migration". This table will replace "events" in 10.0. We need to code together the following:

1. A migration which swaps the two tables
2. A migration that drops the old events table
3. Changes to the code to stop replicating events to both tables
4. A migration which adjusts any foreign keys if necessary
5. A migration which processes any remaining background jobs