Add icons for table column sort indicators

[imcbride]

When a table is used to display a view, we can make the columns sortable. Doing so adds an indicator for the current sort direction. I'm including a screenshot of Drupal's default icon, which I had to include the global styling to get to show. Should we have our own version? This is not a high priority request.

[ghost]

@imcbride - is there any special config thing happening to allow this or can ALL html tables be sorted like this?

[imcbride]

Specific config thing when using the views module with a table display mode.

For tables in content we've used this in the past, but Zeb probably knows a more modern version https://www.datatables.net/