Unit Test Generator

As part of the project_template, I think it would be beneficial to also create a template for unit tests, to instantly provide some minimal coverage and to make it as easy as possible for developers to get started writing more advanced tests.

The biggest barrier to entry is often times just setting all the test framework up, and remembering how to do it.

Two ideas here, not necessarily mutually exclusive:

1. A generic test which loads all known models based on CoderedPage (we already have this list). Loops through them and creates an object with a title and some other basic fields, and asserts a successful GET response. The advantage is that you get free unit tests; the disadvantage is that it would still require writing custom unit tests for actual functionality.

2. Similar to `makemigrations`, a management command `maketests` which creates a boilerplate unit test file for each model that doesn't already have a test file. This would be super easy to implement as it could essentially just copy a python template into the folder. The result would be a basic unit test similar to 1 above, but with the intention that the developer can start customizing it to do more.

As part of this we would also need to provide test tooling in `requirements-dev.txt`, similar to how the sass template works.

While 1 above is a bit "cooler", I think 2 is a more useful approach, as it would give the same coverage as 1, but be a lot easier to understand and add to over time.