CRM-12276 Use default option_value to set default activity.status_id when creating an activity. Created a method in OptionGroup to retrieve this value since one didn't exist.

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* CRM-12276: Changing default option in Activity Status does not change the default when creating an activity
  http://issues.civicrm.org/jira/browse/CRM-12276
Merge pull request #334 from davecivicrm/CRM-12276

CRM-12276 Use default option_value to set default activity.status_id whe...