fix dangling bodies bug
use single function for gravity
add display object class for changing display properties at runtime
add extra informatioon to integrator functions
add circuit and node classes for electricity system
add electricity system
update scenes
remove unused event subscriptions
add light system
improve update handling
use transforms for display, in order to allow layering
add generator and thruster systems
add world scaling (to push velocity limit)
fix connection filtering
add new systems to game
add system update ordering
add new systems
add basic electricity behavior
add generator with fuel and light system
wire up electricity to player motion, set fuel and battery gauges