Bad form for value comparison

[dromer]

All over the code we find examples like:

https://github.com/bbc/brave/blob/b9c8e194e0d409b80269d051087a2aeb45e82f38/brave/inputoutputoverlay.py#L137

Here value comparison is actually written as object comparison. This is clearly wrong. Such statements should be written with == and != not with is and is not.

[moschopsuk]

Happy for any PRs to address this 🙂

I've not had much free time recently to go over and address these.