1118 add browse to help

[dstopp]

• Fixes #1118
• Were any Django, import pipeline, table_schema, or dictionary files modified? Y/N
  • If YES:
  • Database used: opus3_test_210526
  • All Django tests pass: Y
  • FLAKE8 run on modified code: Y/NA
• Were any JavaScript or CSS files modified? Y
  • If YES:
  • JSHINT run on all affected files: Y
  • Tested on Chrome, Firefox, Safari, Edge, and iOS: Y (Remember to test all browser sizes)
  • Tested for race conditions (with delayed API calls if applicable): NA

Description of changes:

• added a menu item to the main help dropdown 'Interpreting Preview Images'
• added a submenu that includes CIRS, UVIS and VIMS preview txt
• click on submenu item will open the appropriate preview image .txt file in a new tab and close the help menu

Known problems: