* Add a tab bar to the top of the Palette window that has two
radiobuttons for "Palette" and "Doodads"
* UI: add the concept of a Hidden() widget and the corresponding Hide()
and Show() methods. Hidden widgets are skipped over when evaluating
Frame packing, rendering, and event supervision.
* The Palette Window in editor mode now displays one of two tabs:
* Palette: the old color swatch palette now lives here.
* Doodads: the new Doodad palette.
* The Doodad Palette shows a grid of buttons (2 per row) showing the
available Doodad drawings in the user's config folder.
* The Doodad buttons act as radiobuttons for now and have no other
effect. TODO will be making them react to drag-drop events.
* UI: added a `Children()` method as the inverse of `Parent()` for
container widgets (like Frame, Window and Button) to expose their
children. The BaseWidget just returns an empty []Widget.
* Console: added a `repl` command that keeps the dev console open and
prefixes every command with `$` filled out -- for rapid JavaScript
console evaluation.
* Added a "menu toolbar" to the top of the Edit Mode with useful buttons
that work: New Level, New Doodad (same thing), Save, Save as, Open.
* Added ability for the dev console to prompt the user for a question,
which opens the console automatically. "Save", "Save as" and "Load"
ask for their filenames this way.
* Started groundwork for theming the app. The palette window is a light
brown with an orange title bar, the Menu Toolbar has a black
background, etc.
* Added support for multiple fonts instead of just monospace. DejaVu
Sans (normal and bold) are used now for most labels and window titles,
respectively. The dev console uses DejaVu Sans Mono as before.
* Update ui.Label to accept PadX and PadY separately instead of only
having the Padding option which did both.
* Improvements to Frame packing algorithm.
* Set the SDL draw mode to BLEND so we can use alpha colors properly,
so now the dev console is semi-translucent.
* 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?"
