Implements Activity Contact validator to check if the logged-in user is one of the Activity Contact Types for a specified Activity ID.

Implements Activity Contact validator to check if the logged-in user is one of the Activity Contact Types for a specified Activity ID.

This allows the "Retrieval criteria for default data" to validate incoming requests for an Activity, checking that the requesting user is one of the Activity Contact Types for the Activity.

Agileware Ref: CIVICRM-2080