Consolidate endpoints for managing OAuth clients

[mostlygeek]

There are two ways to update funnelClients:

1. The admin UI, served at /. The UI has its own handlers GET /new, POST /new, POST /edit/{id}
2. The /clients/ endpoint, GET /clients, GET /clients/{id}, POST /clients/new, DELETE /clients/{id}

This can be consolidated to a single API for remotely managing OAuth clients:

• Update the UI to use /clients/ api endpoints
• Remove the /new, /edit endpoints used by the UI