Added shell for new structural interface material class in order to have a distinct separation between a structural material and a structural interface
Merge branch 'master' of github.com:JimBrouzoulis/OOFEM_Jim
Some small modifications to the structuralinterfacematerial class + started to convert one model to use this class
Merge branch 'master' of github.com:JimBrouzoulis/OOFEM_Jim

Conflicts:
	src/sm/bilinearczmaterialFagerstrom.C