Fixed malfunction probability

See merge request flatland/flatland!297

updated editor to work with persistence.  Modified test rail_env / single_agent and re-enabled.  Added test_env_loop.pkl to go with the test.

Spm/321 group rewards in evaluation service

See merge request flatland/flatland!296

Spm/321 group rewards in evaluation service

See merge request flatland/flatland!293

Pinned PyVirtualDisplay version to avoid bug with pytest-xvfb (https://github.com/The-Compiler/pytest-xvfb/issues/22)

changed the assertRaises to check for ValueError rather than SystemExit when cities cannot be packed in

added some debug (now commented) looking into the shortest path failures.  Now apparently identified / resolved.

switched back to load_resource in rail_env test. passed load_from_package arg down to from_file generators.  switch default renderer to PGL from BROWSER. Added conditional import for flask_util in rendertools to hopefully avoid some startup delays and hanging tests.  Added os.makedirs to intro_flatland 2.1 for saved frames folder.  Removed explicit gl=PILSVG

Spm/318 finegrained metrics

See merge request flatland/flatland!291

Addresses #319 - Add more granular timeouts

See merge request flatland/flatland!290