Canvas experiment: Build order simulator

The demo simulates build orders as of RTS games (e.g. Starcraft2). Here buildorders are very simplified, there is only 1 structure, the central; 2 unit types, worker and knight; and 1 resource, gold. To build those, gold must be paid. Workers harvest gold. Centrals produce units, the more centrals and gold exists, the faster units can be produced. The history of the build is displayed as graph. If the simulation is restarted, history graphs of previous runs are kept and displayed too, this allows to optimize a builder order.