for Coords::QSPACE, dynamically change label Qz -> Qx, depending on alpha_i.
For alpha_i<10deg, leave "Qz". For alpha_i>80deg, replace it by "Qx". In between, say "Qxz".
This is needed because to model SANS we have alpha_i=90.
This is the last little subtask left over from #389 (closed). Wait with implementation so that we can think of other ways to handle SANS.