Disable blended animation (linear interpolation) in css style for crane/arm/crates for now, until I get it working reliably
Add a 'dirty flag' for redrawing crates that have been modified. actually that should be done using a member function
Right, doing it properly, with a member function
Fix a raft of timing/state inconsistencies between running and stepping through the crane program. Introduce a 'fast' mode for the crane for rapid animation  -  in javascript console, set crane.fast = true