ThreeJSForwardTranslator adds unnecessary RenderingColor objects for AirLoopHVAC

[macumber]

Issue overview

ThreeJSForwardTranslator adds unnecessary RenderingColor objects for AirLoopHVAC

Current Behavior

ThreeJSForwardTranslator adds new colors for every AirLoopHVAC even if the expected colors already exist.

Expected Behavior

ThreeJSForwardTranslator should only add new RenderingColors if the expected colors do not already exist.

Steps to Reproduce

1. Call ThreeJSForwardTranslator::modelToThreeJS on a model
2. Check RenderingColors in the model
3. Call ThreeJSForwardTranslator::modelToThreeJS on the same model again
4. Check RenderingColors in the model, note duplicates

Possible Solution

Add code to check if the RenderingColor already exists for the AirLoopHVAC before adding a new object at: https://github.com/NREL/OpenStudio/blob/develop/src/model/ThreeJSForwardTranslator.cpp#L133

Context

Reported at openstudiocoalition/OpenStudioApplication#768