Analytics plugin first pass

OK, I think this is ready to merge for-realz.

Analytics plugin for ubersystem, should be able to drop in for both AC and Magfest no problem.

This is also the first real UI-heavy, database-heavy plugin to be used and those functionalities all seem to work well, which is awesome.

This displays graphs of paying attendance. Excludes: paying dealers, comp'd staff/vip/guest/etc badges, refunded badges.  We want to know how many badges were purchased by the actual general public.

Off the shelf, this plugin displays only the live registration data on a graph (which, is the main point and is super-useful).

However, if you have historical data, you simply drop a json file with the old data in a particular dir in your deploy, and it will merge that with the live data.

There's a few hacky things here (i.e. ANYTHING to do with UI design, responsive, making it look pretty, CSS, etc because I have no patience for that).

@EliAndrewC I'd appreciate a good hard look at my __init__.py to make sure I'm not doing anything too dumb in there with mounting the app config/etc.
BIG NOTE: for this to work, we have to add head_additional in base.html in the core ubersystem repo.  it's in this PR: https://github.com/magfest/ubersystem/pull/763 which also removes the old graph code from core as well as it's being replaced by this code here.