Initialization of FEEvaluation like FEValues

A new way to initialize an FEEvaluation object (fast tensor product evaluation routines) has been introduced.
It takes the same arguments as the initialization method of FEValues, namely a Mapping, a FiniteElement, a
one-dimensional Quadrature<1> object, and update flags. This enables using FEEvaluation on the fly just as
FEValues. Since FEEvaluation treats objects of one base element only, this class can select which components
to read.

The concept is explained in the documentation of the FEEvaluation class and an example for the Laplace matrix
is given. However, it also works for the Stokes operator as shown by the test program assemble_matrix_02.