Donation admin interface should provide graphs and stats of donations

[echarlie]

It would be nice if we got some nice histograms showing:

• number of donations by month
• dollars of donations by month
• donors/dollars by day (during radiothon)
• donors/dollars by time of day (during radiothon)
• donation trends (do dollars donated conform to a normal distribution?)

Some other statistics that would be useful:

• percentage of donors making recurring donations
• number of unique donors
• mean, median of donation size

In this line, it would also be nice if we could export donation data as CSV, only including time of day of donation, dollars donated, a unique donor identifier (hash of email address?), and first-time-donor status, so people can do statistical analysis of donor data.

[mutantmonkey]

This issue is another one of those where there's so much info in it that it's hard to tell what is actually desired. Initial CSV export functionality was added in wuvt/wuvt-site#325.

[echarlie]

we should hook up grafana and build some sample graphs to see what people want.