fix subpixel rending problems, for good this time

by removing the absolute positioning of individual bars and instead
floating left, we make the browser's job much easier
re-institute a two column layout for /about/charts.html
chart JS cleanup
get the X axis working propery
Take out X axis ticks

These were added without discussion.
Clean up whitespace
Fix regression in x axis labels

Weeks are numbered starting with one, not zero.
Correct a comment

We don't necessarily show a chart for every variable available, only for
the ones for which a container exists on the page.
Merge pull request #1761 from gittip/chart-fixes

Chart fixes