Google Code-in

The custom NAS form in the admin of django-freeradius allows to enter a NAS type which is not included in the available options, but due to how django choices work, custom values won't be shown in the admin select list.

We should do the following:

• make the NAS choices customizable with a setting
• document the new setting
• remove the current NAS form and eventual unit tests related to it

Don't forget to start and fork the repository. Open a pull request as soon as you have some code to show but please send it for review only when ready.