Fix SQLite registration bug

[neilalexander]

This fixes two things:

• The error type returned by SQLite on a violated constraint wasn't triggering the upstream code to check for duplicate accounts, causing the registration flow to proceed unexpectedly
• The order of insertions on an account creation has been changed to try the account insertion before the account data/profile

[kegsay]

Wait for CI but this LGTM. This does mean that duplication /register requests for the same user will now fail even if the login credentials are correct, but this is probably fine since the client should be using /login.

[neilalexander]

The sytest failure Local device key changes get to remote servers with correct prev_id is about to be blacklisted in a separate PR, the other tests are green.