* Add ui.Window to easily create reusable windows with titles.
* Add a palette window (panel) to the right edge of the Edit Mode.
* Has Radio Buttons listing the colors available in the palette.
* Add palette support to Edit Mode so when you draw pixels, they take
on the color and attributes of the currently selected Swatch in your
palette.
* Revise the on-disk format to better serialize the Palette object to
JSON.
* Break Play Mode: collision detection fails because the Grid key
elements are now full Pixel objects (which retain their Palette and
Swatch properties).
* The Grid will need to be re-worked to separate X,Y coordinates from
the Pixel metadata to just test "is something there, and what is
it?"
* Add a debug view that draws the player bounding boxes.
* Improve the collision detection to add support for:
* Doodads being "Grounded" so gravity need not apply.
* Walking up hills, albeit a bit "bouncily"
* Harder to clip out of bounds
Known bugs:
* The Pixel format in the Grid has DX and DY attributes and
it wreaks havoc on collision detection in Play Mode when you
come straight from the editor. Reloading the map from disk to
play is OK cuz it lacks these attrs.
