Custom error pages

[reecehill]

Overview

TBC.

Code changes

TBC.

Documentation changes (done or required as a result of this PR)

nil.

Related Issues

#21

[eatyourpeas]

@reecehill I have fixed the broken tests here - please check over to be happy. I put all the error tests into a single class and a single file: hope that is ok.

The permissions tests were breaking because the custom 403 did not explicitly set the error code to 403, so this was therefore returning 200. Hope that makes sense. I have only tested the 403 in the UI, not the 500 or 404 etc.

Also, @mbarton comment here - not sure about the wording in the templates. Phrases like This may be due to a client error or a malformed request. is quite jargon-filled.

Perhaps could simplify the wording for each? I agree though needs to be friendly and where possible offer users option to reach out to NPDA team if they are having difficulties. I wonder if we could get the team to do us a custom background for this, as they did in E12

I am puzzled though because the tests are now all passing for me locally but are still apparently failing on github.

[eatyourpeas]

Tests failing on github:
Process completed with exit code 137.
This means insufficient memory, so not sure why that would be.