Avoid CInstructions in basis evaluations

I previously sticked to the PDELab style here, using mv and axpy and the like. But it is better to expose all of the structure to loopy by using reductions.

This is implemented in all but evaluate_testfunction_gradient.

Might be a good toy project, @rhess . There is plenty of examples how to do it in that module and make build_tests && ctest gives good feedback.