Improve COISS filter tooltip. Fixes #1178.

[rfrenchseti]

• Fixes #1178
• Were any Django, import pipeline, table_schema, or dictionary files modified? Y
  • If YES:
  • Database used: opus3_test_210603
  • All Django tests pass: Y\
  • FLAKE8 run on modified code: Y
• Were any JavaScript or CSS files modified? N
  • If YES:
  • JSHINT run on all affected files: Y/NA
  • Tested on Chrome, Firefox, Safari, Edge, and iOS: Y/NA (Remember to test all browser sizes)
  • Tested for race conditions (with delayed API calls if applicable): Y/NA

Description of changes:

Change COISS combined_filter tooltip.

Known problems: