Parameter distributions inside AlphaScan are now IDistribution1D instead of IRangedDistribution. A first step towards removal of the latter.

We have two similar distribution class hierarchies: IDistribution1D and IRangedDistribution, with all their children. I will resolve this code duplication and ultimately remove IRangedDistribution. This is also a precondition to efficient resolution of #422.

Here, some functionality of IRangedDistribution is copied to IDistribution1D, namely the possibility to set the number of numeric samples and the range from which these samples are drawn.

These changes to the kernel required an unusual amount of adaptations in the GUI. Going along, I also simplified a few other things in the GUI code.

This MR passes all tests, but still breaks things. So far, the new mechanism is only implemented for Gaussian distributions. Necessary clean-up is requested through follow-up issues #437 (closed) #438 (closed) #439 (closed).