Added django-dajaxice and select2 to support autocompletion

tnc-ba/strongTNC#28
Added module that provides global non-model-bound permissions

The approach is based on the stackoverflow answer at
http://stackoverflow.com/a/13952198/284318.
Changed setpassword command to create both readonly and read-write users

Extended setpassword management command with two new features:

- Command now creates both readonly user and admin user
- The admin user now receives the `write_access` permission
Implemented login with two different users

The user can now choose in the login form whether he wants to login as
readonly user or as read/write user.
Fixed broken regular expressions in urls.py

The URL definitions in `tncapp/urls.py` contained some broken regular
expressions (missing trailing slash). This commit fixes these.
Check permissions in backend

Added `@permission_required` checks in all relevant views.

There is now a new test function in `tests/test_auth.py` that verifies
permissions on all the relevant URLs. If new create/update/delete URLs
are added, the test parameters should be adjusted accordingly.
Check permissions in frontend

Form fields are disabled using the new `{% input_editability %}`
template tag.

Other blocks are checked using the following `if`-statement:

    {% if 'tncapp.write_access' in perms %}

PS: Yes, `editability` *is* a word! https://en.wiktionary.org/wiki/editability
Added ConfigParser to settings.ini
Added settings.sample.ini
Updated Travis CI config

With the new split config file we need an additional configuration step
in .travis.yml.
Added TIME_ZONE to settings.ini

Refs tnc-ba/strongTNC#94.
Merge 'Integration Request 3'

Loads elements of dropdowns with many items via AJAX (adds a new
dependency), introduces readonly and read/write roles, and moves some
configuration options to a settings.ini file.

Closes #6.