downgrade scipy version requirement

See merge request !12

We use sparse matrix reshaping, which is only in newer version of
scipy. We want to maintain version compatibility with Kwant, so
we get around this by vendoring the relevant functionality and
monkey-patching scipy.

Fix inconsistency in sympy symbols in Models

See merge request !11

allow 'display_family' to work even in the absence of IPython

See merge request !9

Just fallback to regular printing.

Also add a test that display_family should run when IPython is available

it has been superceded by the kekule tutorial

It has been superceded by the tutorial

It has been superceded by the bloch generator tutorial

It has been replaced by the symmetry finder tutorial

It has been superceded by the tutorial