Finish a cleaned-up/working "who's giving" visualization

Includes both the images for the main categories (and their
relative sizes) as well as an expandible list of top contributors.
finish a cleaned-up/working spending visualization

showing categories and relative amouts as both a bar chart or a pie chart.
The pie chart may need work to tease apart the labels when several very
small slices end up next to each other. For both charts, I went with a
tooltip that shows up onmouseover because we don't have images for all the
possible categories.
Temporarily use a different endpoint URL for transaction data

Sam is investigating the root cause of the mysterious "refresh bug", and
until he patches up the main server, this one seems to be working.