A blank domain throws an error in /theses/.
I've also installed factory_boy (pip install -r requirements.txt
to get it) and set up a ThesisLinkFactory and a unit tests that
tests whether ThesisLink validates for a blank domain field.

Not sure if this is exactly how you're supposed to validate
a model, but it's a start. First unit test of the project, whoohoo!

This is recommended. Also give names like
MASTER_THESIS = 'MA' to avoid magic strings and allow for easy
reference, e.g. thesis.type = ThesisLink.MASTER_THESIS. This sort
of thing helps in maintainability of the codebase, since if we want
to change the abbreviation to 'MASTER' for some reason, we have it
defined in one place, and not in 100 places in the code.

I've opted for hanging indentation

foo = long_function_name(
    var_one, var_two,
    var_three, var_four)

instead of aligning with opening delimiter

foo = long_function_name(var_one, var_two,
                         var_three, var_four)

because the former makes more sense to me. See
https://www.python.org/dev/peps/pep-0008/#indentation