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