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> . Due to this the email stated '$participant_status' in email rather than actual status.

 - the template event_online_receipt_html didn't had participant_status 'if' conditioning, so added that.

The fix had to be done in crm_event_bao_event file has few other files also call 'sendmail' function