Required for a query API which will be used by the syncapi which
will be called when a `/sync` request comes in which will return
a list of user IDs of people who have changed their device keys
between two tokens.
* Add storage layer for postgres/sqlite
* Return OTK counts when inserting new keys
* Hook up the key DB and make a test pass
* Convert postgres queries to be sqlite queries
* Blacklist test due to requiring rejected events
* Unbreak tests
* Update blacklist
