Support borderless panel types.
Allow custom button types.
Fix tooltips not displaying in the pre-shellmap environment.
Allow button tooltip labels to be set by UI logic.
Allow SheetBuilder to be used from mod code.
Add RGBASpriteWidget.
Replace ra logo psd with svg.
Extract mod selector into its own mod.
Update changelog.
Merge pull request #4953 from pchote/modchooser

Overhauled mod selector.