Fixes for matrix regions with no columns.
Utility for creating padded transforms.

Allows construction of matrices that account for padding by pre-slicing.
Utils for exploding outgoing connection keyspaces.
flake8
WIP Filter vertex components.

Adds some regions for the filter vertex, but doesn't pull everything
together yet (hence the failing test).
Finalise value filters.
Merge branch 'new_pacman2_filters' into new_pacman2