finished implementing EnergyError and EnergyNorm

src/elasticity/assemble/DGElasticity.cpp

src/elasticity/assemble/DGElasticity.hpp

src/elasticity/assemble/EGElasticity.cpp

src/elasticity/assemble/EGElasticity.hpp

src/elasticity/assemble/LagrangeElasticity.cpp

src/elasticity/assemble/LagrangeElasticity.hpp