Display values of theta and phi in interactive 3D plots

[Bisaloo]

Interactive 3D plots are good but cannot be included in articles or pdf presentations. It may be good if users could use them to find out the best angle of view and then use it in the static plot.

I will have a look to see if it's possible with the current 3D backend (rgl). If not, it may be worth switching to another backend. With shiny, I'm sure there are plenty of nice js libraries.