Support for changing a PointCloud's pointRadius

[kephale]

I was looking at scenerygraphics/sciview#334 and added PointCloud's pointRadius to sciview's Properties, but it doesn't actually change the visual: scenerygraphics/sciview@a17d4ee

I tried messing around with an extension function that would refill the PointCloud.texcoords but it didnt do anything. Am I missing something or do we need something to refresh PointClouds after changing their pointRadius