CRM-12877, splitting instance postprocess in BAO::create and add, and exposing hooks

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* CRM-12877: Provide api for creating report instances
  http://issues.civicrm.org/jira/browse/CRM-12877
CRM-12877, fixed save-a-copy bug

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* CRM-12877: Provide api for creating report instances
  http://issues.civicrm.org/jira/browse/CRM-12877
Merge pull request #1056 from deepak-srivastava/reportsapi

CRM-12877