Endpoint Throttling

[toastercup]

If Cortex is going to serve more than its internal users (especially if it's going to be open sourced), it needs endpoint protection, in the form of per-client request throttling.

Some questions to answer:

• What should the default throttle rate be?
• Certain trusted applications, like A&R, will be throttled significantly less by Cortex, so that it (A&R, or the trusted application) can handle its own rate limiting. What should the trusted application rate be?