Enable rotation of CategoryAxis tick labels by angle.
Right now only 0 (horizontal), 90 (right), and -90 (left) are supported.
This feature is not well supported and will only work for short strings.

Related to #504
Satisfy the linter
Fix bizzare bug in travis
Address Brandon's concerns. I expect it will mysteriously fail in Travis
[minor] renames, etc
Merge branch 'develop' into rob-vert-labels

Conflicts:
	plottable-dev.d.ts
	plottable.d.ts
	plottable.js
Address Brandon's comments
Merge pull request #1126 from palantir/rob-vert-labels

Enable rotation of CategoryAxis tick labels by angle.