Remove unused stuff in deprecated.py (flatten, some duplication marking stuff).
Update .gitignore.
Implement change_to_local_grad algorithm.

Intended to be applied after preprocessing of forms, at least after expand_derivatives.

Works for multiple layered grads (i.e. grad(grad(grad(f)))) if
the domain is affine, otherwise only a single grad.

When someone wants to do grad(grad(f)) with f in a high order domain
(or quads actually) they'll have to speak up and maybe give a hand
in the implementation of that. It's not much, just a bit messy.
Merge branch 'martinal/topic-algorithm-change-to-local-representation'
Make form_degree argument third argument to enable FEEC notation
as in the periodic table:
  FiniteElement("P Lambda", shape, r, k)
Introduce and rework aliases for the Periodic Table of the Finite Elements.
Alias "Q" for qudrature element has been removed.
Add signature test that fails.
Fix bug where Domain.signature_data returned the label as part of the data.
Change VectorElement signature to take form_degree after dim to avoid breaking too much code.
Merge branch 'logg/topic-periodic-table'