added more complex intersections

Merge branch '147_new_level_generator' of gitlab.aicrowd.com:flatland/flatland into 147_new_level_generator

Much more stable level generation.
Checking for invalid transitions objects and fixing them.

@adrian please fix visuals.. ,)

minor bug fixes in node connecting algorithm

minor bug fixes in node connecting algorithm

All starting positions are valid.
Check for feasibility of map is not yet done.

introduced cities and intersections. These will make up the sparse network. THen you can add trainstations to the cities and populate them with tasks for agents (start/target). Orientation of agents needs to be fixed. Also check for invalid transitions in cities and nodes needs to be implemented.

Merge branch '147_new_level_generator' of gitlab.aicrowd.com:flatland/flatland into 147_new_level_generator

# Conflicts:
#	tests/test_flatland_env_sparse_rail_generator.py

introduced cities and intersections. These will make up the sparse network. THen you can add trainstations to the cities and populate them with tasks for agents (start/target). Orientation of agents needs to be fixed. Also check for invalid transitions in cities and nodes needs to be implemented.