Enable Participation Metrics in the API

[#1]

Allow particpation metrics to be downloaded from the API.  Its great that these are now avialable in DataWarehouse, but these are not in the API.  Will there be plans to add these? 

[#2]

Tagging @JGrover on this.

[#3]

If you have Participation enabled on a metric you can use in the latest version of the API