gait10dof18musc models has Millard muscles but properties for Thelen muscles

[carmichaelong]

Affects all 6 models in this folder: https://github.com/opensim-org/opensim-models/tree/master/Models/Gait10dof18musc

Also affects core files:
https://github.com/opensim-org/opensim-core/blob/master/OpenSim/Tests/shared/gait10dof18musc_subject01.osim
https://github.com/opensim-org/opensim-core/blob/master/Applications/CMC/test/gait10dof18musc_subject01.osim

[carmichaelong]

Also need to keep in mind that we decided to keep 3.0+ style models rather than convert to 4.0+ models in the repo