Started retooling for GPa
Started retooling for GPa

Adopted GPa as the standard EC unit. Added a function to check various aspects of a stiffness tensor.

pusher96/MSAT,jwookey/MSAT,pusher96/MSAT,jwookey/MSAT,alanfbaird/MSAT,pusher96/MSAT,alanfbaird/MSAT,alanfbaird/MSAT,jwookey/MSAT