Feature: add method to add a trimming curve to an already created Grid

[henrij22]

It should be possible to add (additional) trimming curves to an already existing grid, weather this grid was created manually by hand or with the IbraReader.

This feature should also check if the added trimming curves are overlapping with already existing ones. At least it should be looked into the behaviour that arises from that.

To implement this, one has to think about if the curve is to be defined in the physical or the parameter space. A curve in the physical space has to be transferred firstly to the parameter space of the surface. Is a total reparametrisation needed or is it enough to transform the control points.