Space group operations for modulated structures and quasicrystals

[sauliusg]

After the PR for the space group operations is (hopefully) merged, we need to continue and specify 4D and higher dimension symmetry operations for incommensurately modulated structures and quasicrystals.

The approach would be similar to 3D space group operations, using the x1-xn notation (similar to Jones' faithful notation for 3D space groups), e.g.:

+x1,+x2,+x3,+x4
+x1,+x2,+x3,+x4,+x5,+x6
+x1,+x2,-1/2-x3,-1/2+x4
+x1,-1/2+x2,-x3,-x4
+x1,-x2,-x3,+x4,-x5,-x6
+x1,-x2,-x3,-1/2+x4

Modulations vectors and superspacegroup symbols need to be specified as well. The IUCr dictionaries on this topic should be consulted and followed as closely as possible.