Optional parameter to help with stats tracking

[mjcollin]

The API will take an arbitrary string that can be used to identify the source of API calls. It was originally designed for the portal but if exposed and documented we might be able to get others to use it to tie their use to requests.

Check if the source tagging on the API got implimented.

[mjcollin]

This should be all set to go with the addition of "&source=ridigbio" or similar to the request or packed into the JSON posted.

• [ Allow users to override with their own parameter ]
• [ Ask @sckott to do so in spoc ]
• [ Consider packing the ridigbio version number into the default "ridigbio" ]

[sckott]

aren't user agent strings a common way to say what thing is making the request?