let titlebars float over windows, and toggle hide-unhide

[42e6]

when swaybars are hidden, pressing $mod unhides them and they're floaty (they don't scale windows).

titlebars in stacks/tabs should also have this option. i.e. titlebars are fully invisible unless (say) $mod is pressed by which they unhide and show by floating over the window in their stack.

this greatly enhances the utility without bringing any inconvenience, as the tabs unhide whenever (say) $mod is pressed.

this also has to be "floating" to avoid the inconvenience of resizing windows.