Speed up large world updates about planjure

[elben]

The slowest part seems to be updating :world in app-state every single mousemove. update-world can probably be optimized, but not as much as canvas updates. The whole app has to redraw per world update.

Need to use cursors on other components, instead of depending on the whole app-state (which will force components to re-draw for any state change).

[elben]

Here are the timings, the sum over time:

Update world time:  27
Canvas redraw time:  6101
Update world time:  29
Update world time:  31
Update world time:  33
Canvas redraw time:  6969
Update world time:  35
Canvas redraw time:  7798 

[elben]

Made wayyy faster via these commits:

7adf7de
cc7ced9

Got canvas redraw time to ~300ms, down from the ~800ms you see above (those numbers above are sums of all time).