* Ignore all types of coverage files.
I was getting things like `.coverage.$user`.
* Refactor existing serializers.
Some serializers had their metadata all the way at the top
of the file in separate variables, even though no other
serializer were using those variables.
* Put things into proper places to make it easier to read
and change, without having to jump up and down a 1000+
line file.
* Add new serializers and use them in viewsets.
These are the serializers for all 4 new endpoints,
for courses, course runs, programs, and their aggregation.
* Add new mixin for detail endpoint.
The mixin will add `/detail` to the end of whatever viewset
that uses it.
* Call isort on the codebase.
* Refactor serializer test code.
This will make it x10 easier to add tests for the
serializers we introduced in this PR.
* Add test code for serializers.
* Refactor and add tests for viewsets.
