Reorganize code
Moved isochrone graph logic to its own file graph.py. Origin-revision layer's algorithm is now in origin.py, while revision-content layer's logic was moved to revision.py.
Migrated from D5849 (view on Phabricator)
Staging instance, all changes can be removed at any time
Moved isochrone graph logic to its own file graph.py. Origin-revision layer's algorithm is now in origin.py, while revision-content layer's logic was moved to revision.py.
Migrated from D5849 (view on Phabricator)