create method to disable the ColorScale (but maintain shape coloring)

[davelandry]

Expected Behavior

Users should be able to use the color scale logic to fill shapes, but also have the ColorScale be invisible.

Current Behavior

The colorScale method defines both the variable to be used AND the visibility of the scale.

[frabarz]

Related to this: the documentation says for the colorScalePosition property:

Acceptable values are "top", "bottom", "left", "right", and false. A false value will cause the color scale to not be displayed, but will still color shapes based on the scale.

However this is not the current behavior. This also produces an unexpected behavior, as the internal code still expects the ColorScale instance in this._colorScaleClass to have been rendered. This rendering creates a new internal method in the ColorScale instance that is called later, but as the ColorScale is never rendered, the methos is not created, and the code throws a TypeError.