[Feat] Support for button menus

[olivernybroe]

Could be nice with support for buttons which opens up with buttons underneath, also called popovers.
https://developer.apple.com/macos/human-interface-guidelines/touch-bar/touch-bar-controls-and-views

[olivernybroe]

Waiting for thizzers to implement this first Thizzer/jtouchbar#19

[olivernybroe]

@ttveldhuis works quickly and has already made partial support.