Implement Stacked and Clustered Bar Plots 

They descend newStylePlot, which implements the new dataset api.

TODO:
- [x] Make issue to track smarter stacking logic (account for out-of-order case)
- [x] verify jsdoc
- [x] make issue to track adding animations
- [x] make issue to track enabling horizontal mode
- [x] add more unit tests
- [x] make issue to change accessors on NewStylePlot so they get seriesKey
- [x] move the quicktests into standard quicktest format (.js)

Example usage:
```
data1 = [{name: "jon", y: 1, type: "q1"}, {name: "dan", y: 2, type: "q1"}, {name: "zoo", y: 1, type: "q1"}];
data2 = [{name: "jon", y: 2, type: "q2"}, {name: "dan", y: 4, type: "q2"}, {name: "zoo", y: 2, type: "q2"}];
data3 = [{name: "jon", y: 4, type: "q3"}, {name: "dan", y: 15, type: "q3"}, {name: "zoo", y: 15, type: "q3"}];

xScale = new Plottable.Scale.Ordinal().domain(["jon", "dan", "zoo"]);
yScale = new Plottable.Scale.Linear();
var colorScale = new Plottable.Scale.Color("10").domain(["q1", "q2", "q3"]);

var xAxis = new Plottable.Axis.Category(xScale, "bottom");
var yAxis = new Plottable.Axis.Numeric(yScale, "left");
stackedBarRenderer = new Plottable.Plot.StackedBar(xScale, yScale)
  .addDataset("d1", data1)
  .addDataset("d2", data2)
  .addDataset("d3", data3)
  .project("x", "name", xScale)
  .project("y", "y", yScale)
  .project("fill", "type", colorScale)
```
Yeah, I talked this over with Dan and looked at the generated documentation. It turns out the docs only take the first docstring, so going forward we should have all the documentation on the first declaration.