Hotfix for #519.

This addresses the issue, by adding a flag to Utils.Text.writeText
to allow the user to force vertical or horizontal writing (leaving
the flag unset keeps the original behavior of guessing the correct
orientation).

CategoryAxis currently forces horizontal text orientation.
Merge branch 'master' into HEAD

Conflicts:
	plottable.js
	src/components/categoryAxis.ts
Merge pull request #521 from palantir/519-axis-shift

Hotfix for #519.