Added evaldNdxi to fei2dlinelin and fei2dlinequad
Updates of structural interface element class and pertinent classes. Still in development!
Modifed interface element IntElLine2 and added IntElLine1

+ added support for these two elements in vtkxmlexport
Merge branch 'master' of github.com:JimBrouzoulis/OOFEM_Jim

Conflicts:
	src/oofemlib/vtkxmlexportmodule.C