Limit the available 'Add field' options based on the Resource type selected

Currently, all possible 'Add field' options are able to added to the metadata window regardless of what resource type has been selected.

To enhance the user experience, it would be helpful if only the fields necessary to reference the selected resource type were displayed.

Furthermore, if the display indicated which fields were already in use, and the fields that were yet to be used (eg. ticked/unticked, different colours), it could help users to create complete and accurate references.

In turn, reading lists would model academic standards more effectively to students, particuarly first-years who are learning how to reference.