Abstracting urls/emails/securesync protocol

WAAA GITHUB ATE MY COMMENTS :( :(

[depends on localor branch/pull request]

Moved all URLs/emails/securesync protocol to settings.py.  Updated a few (wiki URL, github URL, admin email) to point to new email/locations, and kept one (adhocsync.com), as it's not ready for migration (requires SSL certificate for kalite.learningequality.org and kalite@learningequality.org to be set up)

In doing so, it is now possible to set up interacting "central" and "local" servers on your local machine, with complete interactions (registration w/ emails, securesync, etc), all without having to touch settings.py.  See docs/TESTBED.md for steps to do that.