errorbars on decade rowChart

Equation:

alpha \* 2 \* sqrt( (k/N) \* (N - k) )

where:
alpha = fudge factor to account for fact that events are not indep. Use alpha = sqrt(5)
k = analogue count in the decade
N = number of days in the decade

For code, see: http://jsfiddle.net/gordonwoodhull/yrugrbhq/17/
Errorbars do not clear automatically, so need to add `chart.selectAll('.errorbar').remove()`
