Implement superimposed element feature #592
Description
Enable placing elements at the center of other elements such that they are split during tracking instead of at the lattice level which is error-prone. For example, modeling a BPM at the center of a quad requires splitting the quad into two halves and placing the bpm at the center. If one wants to set the k1 property of the magnet based on the integrated gradient, you need to do it before splitting the magnet in half, or know that the magnet half was previously part of a single element.