Updated structuralInterface classes. Should add test cases and determine if it works correctly.
Converted 'isointerfacedamage01' to the StructuralInterfaceMaterial 'IntMatIsoDamage' - model not tested yet!
Updated IntMatIsoDamage. Note that the tangent stiffness in not computed correctly - the secant stiffness is currently used.
Added test case for element: IntElLine1
Added draft version of converted interface element: IntElPoint