feat(graphs.graphBuilder) Starting stacked area graph
feat(graph-builder) Add stacked-area.
test(graph.graph-builder) Add tests for stacked-area.
chore(graph-builder) Graph builder takes care of adding components.
chore(data.selection) Remove getByField().
tests(data.selection) Add tests for stack.
chore(data.selection) Remove getByField.
Merge pull request #70 from racker/stacked-area

Stacked Area Graph