Removing reference to centre in grid code
Revert "Removing reference to centre in grid code"

This reverts commit c31d15ff72dd143d18337e4ac0ee88376a042b73.
Revert "Removed various references to the Centre object."

This reverts commit b498b781a99127a2e71a3a51086ac7955d941f5f.

Conflicts:
	pimms_apps/qn/components.py