Cleanup static IDP-related views, and add some basic tests.

This is a more complete fix for issue #237 - it puts all idp-related resources under the .well-known/browserid prefix and adds a test to ensure they can be fetched correctly.  @dannycoates r?

I'm pretty sure that the signin/provision pages don't work with the current API.  We could implement them using the client lib, but that's the job of the jelly, right?  I've changed them to be placeholder pages with a link to the docs for now.