Integration Request 3

This pull request includes fixes for all frontend bugs.

### AJAX Dropdowns

Issues: tnc-ba/strongTNC#28

Dropdowns with many items are now loaded via AJAX. This introduces new dependencies.

To install the dependencies via pip (ideally in a virtualenv, if you want a per-project dependency isolation), just run `pip install -r requirements.txt`.

### Introduced readonly and read/write roles

Issues: tnc-ba/strongTNC#31 tnc-ba/strongTNC#74

At the login screen you can now choose between read-only and read-write access. Both accounts require a password.

To initially set the password, run `./manage.py setpassword` and follow the instructions.

### Split config files

Issues: tnc-ba/strongTNC#89

We discussed about different ways to implement local settings files. One possibility would be simple Python files, but that allows for arbitrary code execution. We now settled for a `settings.ini`, either in your config dir or in `/etc/strongTNC/settings.ini`. It is excluded in `.gitignore` by default.

Simply copy the `config/settings.sample.ini` to either `config/settings.ini` or `/etc/strongTNC/settings.ini` and adjust it if necessary.

This commit is also somewhat related to the "localtime" bug (tnc-ba/strongTNC#94) -- the timezone is now configurable in `settings.ini`.