Finish refactoring time series charts.

Finishes the work started by Chris on time series charts. Mostly just a
couple of bugfixes within that.

Author: Dylan Nugent
Implement a data centering option for time series bar charts

This adds an option to time series bar charts to set whether the value
being passed to the bar should be considered the middle, start, or end
of the bar. For instance, if passing values that are set to be end
values, the bar will be drawn so that the right side of the bar aligns
with the time point on the axis instead of the center.

Author: Dylan Nugent