Assembler for global basis transfer matrices

The method assembles the transfer matrx between fine and coarse grids. Assumptions are

• the grids are related but not necessarily direct descendants
• the global dune-functions basis are scalar, i.e., leaf nodes in the basis tree

For evaluating local functions on other geometries a small wrapper is written. For chaining sequencial father geometries another small wrapper is written.

Two unit tests:

• first, test wether the transfermatrix interpolates coefficients from corase to fine for lagrange basis
• second, test wether a jump over two grid levels can be reproduced by two simple transfers