CRM-12495 - cleanup civicrm_task / task_status / project

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* CRM-12495: Vestiges of "Tasks" features remain in tables `civicrm_task` and `civicrm_task_status`, and in a few classes
  http://issues.civicrm.org/jira/browse/CRM-12495
Merge pull request #844 from dlobo/CRM-12495

CRM-12495 - cleanup civicrm_task / task_status / project