Docs broken

[clbarnes]

Possibly my fault, but for tracking purposes:

If you try to build the docs locally, you get hung up on a backport of unittest.mock (only necessary before python 3.3...), and then on importing pymaid.cytoscape, possibly because of py2cytoscape (an optional dependency). Then it gets stuck on importing .graph, which seems to have been factored away but is still used in pymaid.cytoscape.