CRM-12216 Add help on the Activity form for the option to create separate...

CRM-12216 Add help on the Activity form for the option to create separate activity records for each contact during bulk activity creation. (There was no .hpl file for that template, so adding that.)

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* CRM-12216: add an option to create separate activities for each target contacts
  http://issues.civicrm.org/jira/browse/CRM-12216