Offline Event Registration should use the same template for receipt and confirmation as online event registration so that all event info and price set info will be included

Currently we use a different template for confirmation / receipt email when a participant is registered offline (contact -> view -> events tab -> New Event Registration uses CRM/Contribute/Form/ReceiptMessageOffline.tpl). This means that the participant email is missing the following:

• event details like start and end date, location, phone and email contact info for the event
• event fee level OR price set information

We should modify Event/Form/Participant.php so it can also use CRM/Event/Form/Registration/ReceiptMessage.tpl - and hence give the participant all the relevant info.

NOTE: We've had a few people report that Price Set info is NOT being included for ONLINE Registration confirmations if the confirmation is sent when a Pending (pay later ) event's contribution record is updated to Completed. Please check this and fix if needed (Lobo thinks the price set id may be need to be retrieved explicitly since in the non-pay-later flow we get it from the session.)