Merge branch '141-bugfixes' of ssh://gitlab.aicrowd.com/flatland/flatland into 141-refactoring_random_schedule_generator

#141 speed generator first implementation

Closes #141 and #147

See merge request flatland/flatland!153

147 new level generator

See merge request flatland/flatland!154

Merge branch '147_new_level_generator' of gitlab.aicrowd.com:flatland/flatland into 141-different-agent-classes

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

# Conflicts:
#   flatland/utils/rendertools.py

bugfix test_multi_speed

See merge request flatland/flatland!152

fixing bugs on building trainstations and number of agents limited by the number of built train stations

added render show_debug to show agent index - issue 146

See merge request flatland/flatland!151