Issue with ColorScale.getColorForValue() when min === max

[jorgenherje]

When min === max the color scale is not able to call ColorScale.getColorForValue() without crash.

The ColorScale.getColorForValue()-method calls ColorPalette.getInterpolatedColor(normalizedValue) which throws the error.

Seems like the interpolation does not handle min equal max, and this provides error when coloring by parameters. Both when calling ColorScale.getColorForValue() directly and ColorScale.getAsPlotlyColorScaleMarkerObject().

Note: Only tested with ColorScaleType.Continuous

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An example with test data contains parameters where min == max, and the following gives issue:

[rubenthoms]

Fixed by #304.