Bug: Incorrect Error Responses on Failed Leaderboard Creations

[zysim]

We don't have expected error behaviour for creating Leaderboards.

Step(s) to Reproduce

1. Create a Leaderboard with an existing name/slug
2. Create a Leaderboard with missing/invalid fields

Expected Result

1. Existing name/slug should 409
2. Missing/invalids should 422

Actual Outcome

1. Existing names/slugs 500s
2. Missing/invalids 400s

[TheTedder]

* Fetching users:
  
  * Fetching by ID doesn't work; request param validation outdated

Can you elaborate on this? What exactly is the issue?

[zysim]

Can't fetch users by ID because the request validation failed. And it's because the validation is based on an old set of rules.

[TheTedder]

It worked for me when I tried it, at least after making the changes in #215.