Redesign FE interpolation (and get it working again for multi-point dofs)

[blechta]

Original evaluate_dof(s) using ufc::function was replaced by tabulate_reference_dof_coordinates + map_dofs (transform_values since #32). This made it basically defunct for multiple points dofs. Examples

element = FiniteElement("Nedelec 1st kind H(curl)", triangle, 2)
element = FiniteElement("Nedelec 1st kind H(curl)", tetrahedron, 3)
element = FiniteElement("Nedelec 2nd kind H(curl)", triangle, 2)
element = FiniteElement("Nedelec 2nd kind H(curl)", tetrahedron, 2)

which since that do not support interpolation because dofs are multi-point.

Note that these examples in fact currently crash on a trivially fixable assertion when compiled.

How to reproduce:

cat - > e.ufl <<EOF
element = FiniteElement("Nedelec 1st kind H(curl)", triangle, 2)
EOF

python3 -mffc e.ufl

# observe that implementation of transform_values is junk, will not compile

[blechta]

Agreed design goals:

• Add interpolation function to new ufc_function_space struct.
• Must support vectorised evaluation.
• Consider non-affine elements.
• Rename to something sensible, e.g., interpolation_operator