mattdrayer/api-middleware-regex: Support for opaque keys, server API nam...

@chrisndodge @antoviaque, I think I've finally gotten to the bottom of the failing LMS tests.  In troubleshooting I went ahead and added the "server" namespace to the root URI as I mentioned earlier today.  So, @martynjames, FYI that you'll need to update Apros to reflect the new path (/api/server/courses, etc.) after this PR has been merged.

Chris and I discovered that the social metrics test fails due to a failed mock when running the suite via paver, however it passes when running via rake -- very odd.
Hmmm... This doesn't look right. This is Greg's API. Why are we moving this under our new feature flag? user_api is in use on edx prod and we might have a situation where our code is merged, but not activated. In this case, user_api will still need to work.

Can you put it back where it was? Thanks.