This MR improves the configuration for flake8 as follows
- ignore a lot of files that are deprecated
- ignore a lot of warnings we don't have the energy to care about (most best-practice syntax violations...), so we can concentrate on mort important ones (unused imports etc)
and then fixes a couple of wee lint issues in the test scripts.
The idea here is that we should get the flake8 job to pass by ignoring stuff we can't/won't fix (right now), mainly so that future changes can't introduce new violations of the stuff we do care about (unused imports etc). We can reintroduce more thorough checks later.