Done using isort[1], with the following command:
```
isort -rc ./app ./tests
```
Adds linting to the `run_tests.sh` script to stop badly-sorted imports
getting re-introduced.
Chosen style is ‘Vertical Hanging Indent’ with trailing commas, because
I think it gives the cleanest diffs, eg:
```
from third_party import (
lib1,
lib2,
lib3,
lib4,
)
```
1. https://pypi.python.org/pypi/isort
One of the things we need to know for a service to go live is whether
they have at least two users with the ‘manage service’ permission.
So this commit adds a method to the client to count how many users have
a given permission. We can do logic on this count later. But having the
counting done in the client feels like a cleaner separation of concerns.
Meant some refactoring of the way `service_id` is extracted from the
request, in order to make it easier to mock.
