[wlr/taskbar] "active-only" option to get universal titlebar for all Wayland compositors

[freeconst]

At the moment there is a separate module for Sway only. Module "wlr/taskbar" has option "active-first" to reorder tasks, an "active-only" option would be a great solution to filter them. This way the titlebar (with all taskbar actions) can get other composers.