852 - stackedBarPlot now extends from StackedPlot

Mainly to inherit the stack method.  Functionality should be maintained

Closes #852
ok yeah im confused by this too. i dont like the `this._setAttrHashes()` proposal since it changes the functions to depend on state rather than explicit piping around of data. but it feels like between overriding `_paint, _generateAttrHash, and _draw` we have way more degrees of freedom than are necessary. fundamentally we need 2 degrees i think - generate the attrHash and apply it - so why have 3?