Hide project / output / cache files from VS Code

[jwthomson]

Relates to #617.

After some discussion we thought that ignoring some files is a good idea, but hiding files as a tree under other files could be confusing. Most of the files which were proposed for hiding in a tree were config files which are more likely to need to be edited so we opted not to nest them.

[isaacabraham]

@jwthomson is this good to go?

[Larocceau]

check if this can be done with the gitignore instead

[Larocceau]

@isaacabraham, no; we later decided to see if we can use the gitignore for this. I redacted my approval

[jwthomson]

There were some files which are ignored in the .gitignore which someone may wish to edit from within VS code, e.g. user-specific settings files. So I opted not to persue using the .gitignore file as a basis for what files should be hidden.