Implement bare minimum panopoly_users for Panopoly 2.0 MVP

We don't really have any real MVP requirements around panopoly_users, but unless we want to totally break people once we build out panopoly_users later, we should create a bare minimum module that at least:

• Takes all the user related configuration that's currently in the profile
• Panelizes the user entity (#2664572: Add support for User entities was recently committed)