feat(xkeyboard): Switch layout group on click

When serveral layout groups are defined for the keyboard
they can be cycled when clicking on the module.

   For example:

   $ setxkbmap -layout us,sv,fr

Ref #84

src/components/bar.cpp

@@ -478,7 +478,6 @@ void bar::handle(const evt::button_press& evt) {
   }
 
   std::lock_guard<std::mutex> guard(m_mutex, std::adopt_lock);
-
   if (m_buttonpress.deny(evt->time)) {
     return m_log.trace_x("bar: Ignoring button press (throttled)...");
   }