Lattice offset map #130
Description
I recall @Mikolaj-A-Kowalski mentioning that it would be desirable in lattice universes to allow different elements of the lattice to be shifted/offset. For example, this would be useful in adding BWR water channels.
This would require modifying the latticeUniverse, but probably not very much. This could have an optional input for an offset map, the elements of which would be the 3D shift vectors at each position of the lattice.
I imagine there are also certain circumstances where we would like to not apply the lattice's default transformation as well, e.g., for a lattice containing another lattice with a different pitch. This might require a special syntax.
Are there any neater ways of doing this or does this approach sound reasonable?