fix for : js break when adding new participant through contact screen

Details for replication : 
 -  click on 'Add Register Participant' button in the Events Tab of User Contact Page.
 -  issue error : <code>TypeError: CRM.buildCustomData is not a function
                CRM.buildCustomData( 'Participant', 'null', 'null' ); </code>
 - This is generated because the function invoke is made prior to the function declaration.
 - As a result it breaks all subsequent js in the 'Register Participant' dialog box and the flow breaks.

fix : to declare the function (i.e to include the common/customData.tpl) above the invoke.
causing commit : https://github.com/civicrm/civicrm-core/commit/1beb268a63e70974a25de6f08812575f7f11d778#diff-122c31296531d2f3f77a8920f8f6488bL599