The repository configuration form had a couple of breakages due to

changes made in Django since 1.6. There were two main issues:

Client-side validation of hidden subforms (for hosting services and

SCMTools that aren't selected) and server-side attempts at setting an

immutable dictionary.
The client-side form validation issue is going to be common amongst some

other forms in our codebase (such as the authentication settings form),

and a proper fix is a larger project, but to get things unstuck we're

now turning off required attributes for fields by setting

use_required_attribute on RepositoryForm and the subforms. A better

solution going forward would involve swapping out any fields that are

hidden.
The server-side issues stem from our need to set certain values in the

POSTed form data while cleaning the form. Typically, there's no need to

ever set this data, and on modern versions of Django the form's

dictionary is generally immutable (as it comes from request.POST,

which is immutable on 1.11).
RepositoryForm is more complex, since it can fail to save a repository

but still successfully create intermediary objects. For instance, you

can successfully link an account but not validate a repository. In these

cases, we have certain fields that we want set back in the form data so

that they'll appear as selected values when next rendering the form.
We now check to see if we're using a MultiValueDict (the base class

for QueryDict, which holds POST data), and if so we convert it to a

standard dictionary so we can write to it.
This should fix the form's behavior when running on Django 1.11.

Unit tests pass.
Successfully created repositories through the admin UI.