* When editing a doodad in the Editor Mode, the toolbar has a "Lyr."
button that opens the Layers window.
* The Layers window allows switching the active doodad layer that you
are drawing on, as well as create and rename layers.
* With this feature, Doodads may be fully drawn in-game, including
adding alternate named layers for animations and multiple-state
doodads.
* Update the Pager component to have a configurable MaxPageButtons.
Controls that have more pages than this limit will stop having buttons
drawn after the limit. The "Forward" and "Next" buttons can still
navigate into the extra pages.
* Refactored and centralized the various popup windows in Editor Mode
into editor_ui_popups.go; the SetupPopups() and various methods such
as ShowPaletteWindow() and ShowDoodadDropper() make management of
popups simple for the editor_ui!
* The Menu Bar in Editor Mode now has context-specific tools in the
Tools menu: the Doodad Dropper for levels and Layers for doodads.
* Bugfix the Palette Editor window to work equally between Levels and
Doodads, by only having it care about the Palette and not the Level
that owns it.
