Add Resource icon button should change to checkmark when added

[acharliekelly]

This was issue #167, fixed with #199. New CSS seems to have brought it back.

Expected Behavior

On admin view, clicking the + icon on a resource (on OrganizationCard) should change the icon to a checkmark, so user knows the resource has been added

Current Behavior

Currently, as before #199, the + button toggles to a - and back. No checkmark.

New Behavior

When you click the + icon, it will add a resource and change the icon to a checkmark. But if you hover over the checkmark, it will change to a minus sign, so it's clear that clicking again will remove the resource.