Add a logout feature

Now if it were possible to log in.

New site routes:
- `site.account.logout`: /logout

New packages:
- `gameshaft.tests.views`

New modules:
- `gameshaft.tests.views.account` (Test suit, setup.cfg updated)
- `gameshaft.views.account`

Template changes:
- `core/base.mako`: Update logout link for authenticated users
Database Model Cleanup
Introduce back-end view logic for logging in users

This affects mainly the authn subscriber, the account view and their tests. It also introduces new dependencies in the form of passlib, py-bcrypt and mock.
Cherrypick the requirements.txt changes from commit e69bfd
Add a login form to acccount/login.mako
Fix a mako syntax error in account/login.mako
Actually give the fields in account/login.mako names
Enable Beaker, and fix login/logout links
Merge branch 'feature/1-user-login' into develop

Conflicts:
	config.ini
	requirements.txt