Show Unused Custom Types in Actions

### Is your proposal related to a problem?
I am unable to easily see which Custom Types in Actions are unused. When I refactor a type name for example it will keep the old name in Custom Types even though no Action is using it.

### Describe the solution you'd like
I'd like a visual cue to show which types are not used by any Actions. Also it would be much better to also show which Actions are using each specific Custom Type with a link to each.

### Describe alternatives you've considered
N/A

### If the feature is approved, would you be willing to submit a PR?
I'm afraid I am not versed in Haskell at all.

Start by locating the Actions Custom Types interface and how it represents type usage. The work is complete when unused types have a visible cue and each used type lists links to its Actions; no files or tests are named in the issue.

Written by the indexing model from the issue text.