Consider addition of a /donor set of endpoints

[lottspot]

As our next step is to introduce donor classifications, it may be worthwhile to introduce a new endpoint which is geared toward accessing information about donor classes. Consideration of this endpoint should include musings such as:

• Is there anything that donor specific endpoints may provide that cannot be just as easily gleaned from endpoints which provide CampaignSummary objects?
• Would such an endpoint be useful to the frontend team?