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)
```
Not sure about the formatting policy on html files.  Should we enforce indentation on nesting?  In which case, window.onload should be indented to the right and the js should be indented twice to the right.