Allow users to add additional scripts and stylesheets

[BenSurgisonGDS]

Changes

• Add an additional block to allow users to add their own global scripts
• Add additional blocks to allow users to add their own page and global css

[nataliecarey]

We've discussed doing this, I think it would be helpful but I'm also nervous about customising the layouts because:

• It could conflict with a future change in Frontend
• It dilutes the use of the kit as a place to experiment with Frontend

I think we should start by discussing this with the Design System Team, then if they don't think it belongs in Frontend we should discuss whether it belongs in the kit. If we don't add it to Frontend or the kit then people who want to work around this should be able to use a plug-in to get the same behaviour.

[joelanman]

we currently cover this using the super() function right?

https://prototype-kit.service.gov.uk/docs/adding-css-javascript-and-images

[joelanman]

might this be better as an issue? Then we dont have to keep the code updated and it better reflects the situation as one we're discussing