Banner svg fixes
wrap finite element creation to support quadrilaterals
redefine FunctionSpaceBase._dofs_per_cell

It used to be the vector of DoFs per entity dimension per cell,
but only their sum was used.
Now it is a single number representing the sum.
make _dofs_per_entity calculation quad-compatible
save mess before further experimentation

DO NOT PUSH THIS COMMIT!
reordering mess
fix CG2
fix CGn