Add ModelBackend for future use of mapping django and ldap groups

Enabling it does not affect the authentication, users that are in DB but
not in LDAP (or if connection to LDAP is impossible) can still not
authenticate.

Also, remove useless debug symbols
Check that the activation token consists only of letters and digits
Convert the successful activation message to SUCCESS level message

Add levels in all assertMessage calls in the tests
Improve the regexp to get the exact length and type of chars of the
random token string
Add shebang in setup.py, add okupy.egg-info in .gitignore
Create dirs for the tests and move the existing ones to integration/
Better handling of rendered templates tests
Catch database exceptions, add tests when there's no DB connection
Use assertRegexpMatches
Add coverage and coveralls.io support
Add coveralls badge
fix the travis-ci command
Omit test/__init__.py from coverage, it never gets run
gitignore more files
move the pycrypto imports inside the functions

This way we can get rid of the pycrypto hard-requirement, till those
functions are actually used in the webapp
Packaging updates:

- Add more static files in MANIFEST.in and setup.py
- Categorize the dependencies in setup.py
- Remove non-hard dependencies from requirements.txt
Remove LoginError and SignupError, they served no purpose
rename dictionary to avoid confusion with the function name
Add test to check if already authenticated user gets redirected to /
End the session after 15 minutes of inactivity