Release version 0.28.0
Using accessor instead of accessing data directly
Merge branch 'release-0.28.0' into bugfix-stackedBarAccessor

Conflicts:
	plottable.js
Merge pull request #975 from palantir/bugfix-stackedBarAccessor

Using accessor instead of accessing data directly
Stacked Bars have animations again!
Merge pull request #976 from palantir/bugfix-stackedBarAnimation

Stacked Bars have animations again!
Clustered Bars declare they have no animations
Use null animator if none is declared
Merge pull request #977 from palantir/clusteredBarFix

NewStylePlots default to a null animator
Fix type signature for some ordinal scale functions.
No JS changed. NOQE
Regenerate build artifacts for 0.28.0.
Merge branch 'release-0.28.0' into develop

Conflicts:
	bower.json
	package.json
	plottable-dev.d.ts
	plottable.d.ts