Proper user management on the whole portal

Until now (in `master`), it was only possible to register / log in to Policy Compass from embedded Adhocracy discussions. This PR fixes #50:

- Make sure Adhocracy is always embedded (in order to keep login state synchronized and have correct login state on initial login)
- Add a couple of simple views which just embed Adhocracy `login` / `register` / `adh-user-indicator` (for logout) directives.

This is already deployed on the development server.

There's an issue with logout, but this is tracked separately in #59 in order to move things forward.