[AL] Move switch-case into element loop.

This results in fastest (in number of read instructions) code.
Add missing include.
[AL] Add back addToGlobal() in VectorMatrixAsm.
[T] Add GlobalMatrix/Vector to SteadyDiffusion2D example.
[PL] GW: Add LocalAssemblerData skeleton.
[PL] GW: Fill init, assemble. Add shape matrices.
[AL] Add LocalDataInitializer.

This adds a mapping from element types to the
corresponding shape functions. The latter are
passed as a template parameter to the
LocalAssemblerData.
Merge branch 'GWPLocalAsm' into develop