Revise the Field Configuration Options

The field configuration options for the "list" values are currently very confusing. See the before and after pictures. This patch change this UI to use a bit clearer terminology. The default value for the list field is only shown if the custom list field is enabled at all.

We do loose one particular combination with this approach: Hide all all files by default and enforce the default. However, this doesn't matter since you can easily configure the formatter to use "" to accomplish the same goal. I think this would likely reduce the amount of accidental configurations where administrators hide all the uploaded files.