Add toggle `CategoryAxis.textOrientation` 

Allows you to set text orientation.

Added quicktest.

Close #504 although I think we should do some testing of whether the vertical alignment option works very well (tkim could you play around with it and see if the behavior is up to par?)

Conflicts:
	plottable-dev.d.ts
	plottable.d.ts
	plottable.js
	quicktests/list_of_quicktests.json
right now it auto defaults to horizontal, later auto will not be a fixed value but will instead try both and go with whicehver one is better according to some metric (e.g. fit in less space with fewer word breaks)