Include cases and case activities in dedupe merge process

The dedupe merge process (civicrm/contact/merge) needs to be enhanced to detect case record(s) which need to be merged from the duplicate contact into the main contact. Users get the option to merge or not merge all Cases for the duplicate contacts. When case(s) are merged, all associated activiites for the case(s) should be moved along with them.

(... in other words, users can NOT choose to move cases without their associated activities)