Added Lua support for foot-bot distance scanner.
Added Lua utility functions to open and close a robot state table, preventing different devices writing on the same table to overwrite each other's data.
Added differential steering default sensor.
Used new open/close robot state table for Lua. It works when used with the differential steering sensor. Now all the other devices need to be updated with this function.
Fixed definition of wheeled entity and differential steering default actuator.
Added sensor compilation.
Added more sensor compilation.
Added new logic for gripping in the 2d dynamics engine. This new logic not only is better and cleaner, but it also solves a few memory corruptions when removing entities that are connected to others.