Add Site Admin UI to manage API keys

As we add more API features more users will want to use the API. Right now giving a user an API key requires a manual update in the database. We should add a new page to the Site Admin tools that:
1. shows all users with API keys -- including the API key (these are not secret to SAs)
2. allows deleting a user's API key
3. allows provisioning a user a new API key (as an auto-generated UUID)