reworked magnetic constraints; new ISODISTORT visualizer

[briantoby]

GSAS-II has always had the ability to set up pretty sophisticated constraints, but the code to set up constraints between the chemical phase (neutron scatterers tend to call this the nuclear phase) and a magnetic phase, was either broken or was never finished. Now when one uses the manual General/Compute/Transform menu command or a magnetic CIF (at least one from ISODISTORT), the unit cell, the shared atoms and (when hisograms are defined & shared) the phase fractions & isotropic sample broeadening are all constrained to be the same.

While at it, ISODISTORT magnetic deformation modes are now supported via CIF import, in addition to displacive and occupancy modes (but not currently strain or ADP modes).

Finally a new viewer has been created for all "New Var" constraints, but especially the one created for ISODISTORT modes, where one can play with the mode values and see the atom parameters change:

If this is opened from the "Draw Atoms" tab, the visualization changes, tracking the modes.

This is still a work in progress. More testing is needed, especially with displacive and occupancy modes as well as user-supplied modes.