fix(api): small handler bugs found while documenting the API (#262) #1102

Found while documenting the API in #262 (PR #1100). These are code bugs, not spec gaps, so they were left out of that PR:

1. Analytics validation: an unsupported analytics interval or dimension value returns 500 instead of 400.
2. Registration approval: approving a registration can leave it approved with no cloud account when the account creation fails afterwards. It isn't atomic.
3. Account update: PUT /api/accounts/{id} doesn't save provider.
4. Email revoke form: its POST always gets 401.
5. Azure revokes: these probably return 500. This is unverified.

Each needs its own small fix and test; split this issue if that's easier to track.