Add remaining calculations to election summary page

[ckingbailey]

Per @elinaru's mock

Add the remaining calculations to the elections summary page:

• [x] Who is contributing to races on this ballot?
• [x] Candidates with the largest proportion of small contributions
• [ ] Top 5 spenders who have made the most large contributions
• [x] Where is the money coming from?

@tdooner has added dummy data for this on the backend from which we can create the frontend views for these calculations while the backend team works on getting the real data.

Here's a screen shot of the mock for easy reference