LPUB - Grey out previous step

[Gerald Lasser]

I peered a bit into the LPUB code myself. It is certainly something that could be added as LPUB itself is using some a similar method to pinpoint submodels and point an arrow to them. To do so LPUB renders everything in white, just the added sub-model is blue.

I have not yet managed to compile it properly with QTCreator 4.6 so I am still trying to get at least the compiler to run first....