Add a new settings button widget

Implemented and pushed. otter-config-types a4f53e8 defines the static settings-button preset; otter-bar 5afaba9 routes button_settings through the existing generic button widget with a gear icon and otter-settings command; otter-settings 2bd6446 exposes it in the bar widget picker and Buttons editor. ReleaseFast tests pass in all three repositories. It is opt-in and is auto-enabled when added to a layout.