Class AddToCampaignHandler - handle the AddToCampaign action.
A form action to return from geCMSActions or otherwise include in a CMS Edit Form that has the right action name and CSS classes to trigger the AddToCampaignHandler.
Campaign section of the CMS
Warning: Volatile API as placeholder for standard "GridField"
Handles adding the "Add to Campaign" button to a page's secondary actions menu