Feature: Add % to summary statistics

[brianwarner]

It would be helpful to have a % view of summary statistics by time period.

However, it should be presented in a way which doesn't comingle the % with the raw numbers, so it doesn't confuse Excel when copying/pasting results directly from the website. Possibly a set of radio buttons that allow you to select the view: "raw numbers", "%", or "raw numbers (%)"