Prevent labels from wrapping.

This involves changing the default spacing for labels.
clean up reference/comments
use "&#160;" instead of "&nbsp;"
try dropping width again; there is a bug :(
fix issue #494 & expand xAxisLabelWidth; lots of failing tests
Change x-axis pixel spacing default to 70.

Also updates tests. The cases where we get one axis label instead of
seven are a bit troubling.
Merge pull request #484 from danvk/wrapped-labels

Wrapped labels