Put common preProcess actions into parent class

Put common preProcess actions into parent class

Note that this switches the Participant form to calling
      CRM_Contact_Form_Task::preProcessCommon($this);
      rather than parent::preProcess();
      I think this may remove the need for the twisted inheritance
      but haven't set AbstractEditPayment back to inherit from
      CRM_Core_Form
      which is more desirable.y

towards consolidating onto parent preProcess
but the whole cdtype seems to block tidy up - although cdType seems to be a misimplementation -
in that there should be a custom data type form called for ajax rather than putting it on every form

r

r