* Add the other trapdoor directions: Left, Right and Up.
* UI: Show a color square in each Palette Swatch button in Edit Mode.
* Instead of just the label like "solid", "fire", "decoration" it also
shows a square box colored as the swatch color. The label and box
are left-aligned in the button.
* Minor Play Mode physics update:
* The player jump is now limited: they may only continue to move
upwards for 20 ticks, after which they must touch ground before
jumping again.
* Remove the "press Down to move down" button. Only gravity moves you
down.
* Fix a crash in the Editor Mode when you dragged doodads on top of each
other. Source of bug was the loopActorCollision() function, which only
should be useful to Play Mode, and it expected the scripting engine to
be attached to the Canvas. In EditorMode there is no scripting engine.
