Refactor HTMX Viewsets

[shapiromatron]

Refactor our lit.workflows and assessment.attachments HTMX ViewSets to use new .show-only-child class and remove nearly-identical templates between eco and epiv2 viewsets.

• show-only-child hides an element unless it is the only child of a parent element
• hide-empty-table will hide an element unless it has a child <tbody> containing a <tr> element
• Fix deletion script for eco class; cascading deletions are now properly displayed in the eco update page (i.e., deleting a Cause will immediately remove related Results from the table)