Show explanations for visible test cases

**Is your feature request related to a problem? Please describe.**
There is no clean way for a host to explain test cases, it would be nice if they could on a case-by-case basis.

**Describe the solution you'd like**
Add a note after a test case in the questions pane that shows the reason for the test case

Start by tracing the questions pane and how visible test cases are represented. Add a per-case explanation supplied by the host, and verify that the note appears after the relevant test case without affecting other cases.

Written by the indexing model from the issue text.