Move chart styles up into SCSS

The styles for the charts on /about/charts.html were defined in a
<style> block in the simplate. Now we want to use those styles on a
chart on another page (#1514), so let's move them into the global
stylesheet.
Forgot this file
Move chart js to it's own file

Next step is to make it a proper library.
Four of the six charts are reimplemented

The two that aren't are cumulative and nwithdrawals, which need some
math on them. These are the existing charts, mind you. Once these are
taken care of I'll look at implementing the per-user chart.
Implement withdrawals chart

I decided to move the calculation to the server-side rather than
complicating the chart API on the client-side. This introduces a new
endpoint, /about/charts.json.
Implement total gifts

I did this as a subselect in the charts.json query.
Fix regression in Weekly Gifts chart

I was using the wrong column from paydays.
Rough in the per-user chart of receipts
Scale per-user chart to full Gittip history

The way we do the X axis in the chart kind of requires this. I guess it
also makes it easier to compare across users and with the overall
system.
Rename js file to match Gittip.charts namespace
Move chart into place on user page
Reformat a comment
Prune old code
Fix curly braces
Change from Gifts to Receipts for user chart
Prune extraneous comment
Fix regression in user chart w/ file rename
Add Number of Patrons chart; #1514
Only show one max flag on charts
Change "Weekly Receipts" to "Receipts"

The "Weekly" is redundant (on the about/charts page it is to distinguish
from cumulative gifts), especially next to "Number of Patrons."