CRM-12924, CRM-12940 pluging advanced search panes via queryObjects hook

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* CRM-12924: Implement "Job" search (for "Advanced Search")
  http://issues.civicrm.org/jira/browse/CRM-12924
* CRM-12940: Allow extensions to participate in CRM_*_BAO_Query
  http://issues.civicrm.org/jira/browse/CRM-12940