Set up some basic models.

I haven't even created the migrations yet since these models are still
in progress. This is just for testing purposes so far.

`UserProfileMixin` is from meaningfulconsent.
I'm not sure what the SOCW ID is, looking at this page (http://wiki.ccnmtl.columbia.edu/index.php/WORTH_2_User_Stories) each participant will have a Study ID, each Facilitator will have a Facilitator ID. I've separated out Participants and Facilitators into separate models each using `UserProfileMixin`.