Enable "width" projection for range-band-backed BarPlots.
Also refactor BarPlot code to move logic into the base class.
Also make Plot.project() automatically call _render.
Merge branch 'master' into bar-width-projector

Conflicts:
	plottable.js
	src/components/plots/abstractBarPlot.ts
	src/components/plots/verticalBarPlot.ts
	test/rendererTests.ts
	test/tests.js
Fix the bug that Cassie found where on bands-mode scales, bars are out of
position if you project width explicitly
Merge pull request #584 from palantir/bar-width-projector

Enable "width" projection for range-band-backed BarPlots.