New object: conveyor belt

[kaa-ching]

Requirements:

• [ ] Must be horizontally stretchable by players
  • does not need to be tickless, increments of e.g. 25 cm is acceptable
• [ ] Need to think about a concept to drive it, e.g. engines. Or make it self-running for now.
  • custom dial to set the speed?
  • problem: it would add considerably to the level enjoyability (read: more possibilities for puzzles) if users can drive the belts using other things.
• [ ] Bottom side must work, too (e.g. for balloons)
• [ ] At least 20cm high There's probably more requirements - let's think about those.