Implement Aggregate date granularity in Overtime and Trended Reports.

I came across this issue this morning.  I needed to utilize the aggregate date granularity available in the API.  The API uses the aggregate granularity by not passing a date granularity in the JSON request object.  I have implemented this in this pull request.  This should be no compatibility issues as I just do not set the date granularity parameter when a granularity of "aggregate" is passed in. 

Thanks,
Jason