Allow user to define list view fields in config

[benmatselby]

For the submission and study list views, we allow the user to specify the fields they want to show. This is very flexible, but if you want to have more fields other than the default, this is a little messy.

I'd recommend the ability to define these fields in the config, and check to see if it's defined in the list view commands.

Order of precedence:

• Check env vars
• Check config
• Default to standard fields in code