CRM-13890 : participant_status

few things were missing in message_template hence needed update : 

 - the template variable  'participant_status' in event_online_receipt_text template was not used properly i.e. correct - <code>{$participant_status}</code> ; incorrect - <code>$participant_status</code>

 - the template event_online_receipt_html didn't had participant_status 'if' conditioning, so added that.

T