Make display of N/A consistent

[acoffman]

Instances where N/A is manually selected should continue to display as they currently do.

Instances where N/A is enforced (ex: the user is never given a choice to select a disease for functional evidence) should display N/A but visually differentiated somehow (grayed out/tooltip).

This should apply to browse grids, evidence grids, and search results.

More details in the 5/6/21 meeting agenda.