852 - stackedBarPlot now extends from StackedPlot

Mainly to inherit the stack method.  Functionality should be maintained

Closes #852
This is some pretty silly nesting of _underscored calls. Right now it looks like this:

```
public _paint() {
  <class-specific setup>
  this._draw(); // same for all classes
}
```

It might make more sense like this:

```
public _paint() {
  this._setAttrHashes(); // overridden by any classes that need to
  <logic from _draw() >
}
```