Refs #68; Finished Heatmap Option Testing

In addition to finishing the testing, I also added the following:

- `option:cutOutliers` event listener
- Changed the name of `@colorFn` to `@opacityFn`
- Pulled color function from option setting out of the constructor and into new method               `_setOpacityFunction`
- Fixed outlier removal in the bucketing method
- Fixed `option:opacity` event listener