index.html: info panel div
js/things: new storage, draw mechanisms...

- store thing instances in an object instead of a grid
- loop over this object in draw (much quicker)
- new `nearest` function, find Thing in store nearest passed point
- new hasThing, might be redundant...
- Thing can be marked as `selected` changes coloiur and call TSG.info

TODO:
- save/load thing store
- genes, movement rules etc.
js/stuff: `hasStuff`, `killStuff` altered to take array point
js/tsg: on click, find nearest things, call `info` to update panel. simplfiy `draw`, call thingMgr.draw for things