Gaussian blur transparency of outline

1. A concise explanation of the problem you're experiencing.

The current outline material of line don't support gaussian-blur transparency, I want to show polyline with gaussian-blur transparenct border.

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

4. The Cesium version you're using, your operating system and browser.

Hi Tristan,

Try the PolylineGlowMaterialProperty.

See it in action in this Sandcastle example.