Moved material transition code to a separate subroutine and tweaked it to check again for transitions after chaning the material number

Added option of defining a dominant material type that will define the element material properties if any volume is present within an element

Added test to ensure the transum values for material transitions are less than or equal to the number of defined materials

Moved compute_plastic_params subroutine from vrm.f90 into a separate file. It is no longer called by DOUAR as it was not doing anything unique. vrm.f90 handles all of the plasticity parameter calculations now.