This options enables to generate jacobian apply methods regardless
of the `matrix_free` option. If `matrix_free` is set to true,
`generate_jacobian_apply` is also set to true. This option replaces
`matrix_free` in all contexts except in the selection of the solver.

Needed in dune-perftool-playground for Navier stokes

Note: Not yet working for gmsh files

We previously used bool() on the constraints expression to find
out whether we need to use the DIrichletConstraintsAssembler.
However, UFL does the stupid thing of evaulating

bool(eq(x[0], 0))

to False, because x[0] and 0 are obvioulsy not the same. Veeeery
bad behaviour for a symbolic language.

We do this from multiple subdirs