Merge pull request #1159 from palantir/stackedArea0

[Hotfix --> master] - Stacked Area with 0 valued datum uses the positive offset value
Merge pull request #1165 from palantir/emptyDatasetFailure

[Hotfix --> master] - [StackedArea] - Projection logic allows for empty datasets
Release version 0.32.1
Release v0.33.0-preview
Release version 0.33.0
Merge branch 'release-0.33.0'

Conflicts:
	bower.json
	package.json
	plottable.js
	plottable.min.js
	plottable.zip
Merge pull request #1184 from palantir/master

Master --> Develop to pick up v0.33.0