Modifies constant penalty calculation to provide equivalence with element-wise calculation

[srwopschall]

• The constant penalty calculation was not commensurate with the 'model' used in the element-wise penalty calculation
• This PR modifies the constant penalty calculation to follow the spring-in-series model used in the element-wise calculation.
• This allows a user or developer to compare behavior when using the two penalty types under the condition that each mesh's penalty stiffness is equivalent across penalty types. (E.g. bulk_mod/t = 1, constant_penalty = 1).