[applets/systemtray] Add a button in the hidden view to show the config window
requested to merge ngraham/plasma-workspace:give-the-systemtray-a-big-fat-pin-button-that-you-can-touch into master
Without this, the only way to show the config window for the System Tray itself is by right-clicking, and as we all know, this is a no-no because many users don't right-click on stuff and you can't right-click at all on touch and we want our stuff to work on convertible devices with touchscreens. So let's add a big beautiful button that people can click on and touch.
cc @teams/vdg