Extend std analyses with callback funcs

This allows for calling Star-specific instructions from within these analyses without introducing some dependencies to libStar. Otherwise, the solution would be to "simply" duplicate these two analyses inside libStar.

P.S.: note that derived "StarScurveFitter" and "StarNPointsGain" analysis objects (an upcoming MR) still need to be registered in StdDict, which is WIP (this is so far done by ScanHelper but I still need to find a way not to create a libYarr->libStar dependence, which is not so easy) but that's a different topic...