Set array length to number of integration points.

Typedefs. Constness.
[AL] Extend SerialExecutor and SimpleAssembler by variadic args.

This allows passing arbitrary parameters to the concrete local assembler
implementations.
Add init function to LocalGWAssemblerData.

Copies the previous implementation of ShapeMatricesInitializer.
Make ShapeMatricesInitializer Data independent. Rename.

LocalDataInitializer calls the data's init() method for initialization.
[AL] Use local matrix/vector types from assembler.