Date ranges break on dash

Previously, non-breaking-spaces were used adjacent to date spans when
Elroi constructed a date range.  This caused inconsistent behavior across
browsers; where Chrome and IE would break on the dash, Firefox would not.

In the case a browser didn't break, it was possible that the date-range
labels of a graph would overflow onto each other.  To achieve consistent
(and desired) date range breaking behavior, breaking-spaces are now used.

This will avoid the overflow issue across all supported browsers by
always allowing a date range to break on the dividing '-'.