Fix database indices

[BenjaminPelletier]

Currently, the indices we are using for many of our CockroachDB database tables are suboptimal; we should update our indices to optimize performance, storage, and probability of success.

Some indices are not used in any queries. Only one index is used when SELECTing data, but sometimes we have indices on each of the columns used in the WHERE clause. It is an anti-pattern to have an index on a sequential key like timestamps.

It is likely this will improve #742