Feature/tab submodule tests

The actual modules that sit inside a tab weren't being tested as their own module type.
Now the test runner clicks through each tab and tests the child module.

### Notes:

* Student finance is currently broken, so possibly add it to the ignore array in config before testing.
* G-Cloud will rely on https://github.com/alphagov/spotlight/pull/362 to pass, so either run against that branch, or go merge that first.