This is a quick commit. I gave admins the ability to ban or unban users

This is a quick commit. I gave admins the ability to ban or unban users
straight from the moderation.users_detail page. I also changed the
UserBan.expiration_date type from DateTime into Date. I also began work on the
Terms of Service, pulled from another website (which will be cited clearly
before I'm done). I added new tests as well for the ban/unbanning. Lastly,
I added a few `user_not_banned` decorators to relevant views, so banned users
cannot access any pages.