Allowing custom endpoints on the 'Client Configuration' page

Hey,
we needed a custom endpoint setting in our sentry server and we thought it would be a good a idea to share.

Our client doesn't send errors straight to Sentry, instead it goes to a frontend nginx if it's a javascript error or to our cyclops server.

That makes our sentry server scalable since we can grow only our javascript error collector if we need to, but for that to work we need to show this url on the 'Client Configuration' page instead of the default sentry url.

Besides that we when it's a backend project we use a different endpoint, that points to our cyclops server.

We've added two new settings, that can be used like this:

SENTRY_ENDPOINT = 'http://cyclops.internal.com'
SENTRY_PUBLIC_ENDPOINT = 'http://js_error_collector.public.com'