feat(xwindow): New module "xwindow"

Add module to display title of active window.
Requires WM with support for the _NET_ACTIVE_WINDOW hint.

Ref #84

src/modules/xbacklight.cpp

@@ -61,6 +61,13 @@ namespace modules {
     update();
   }
 
+  /**
+   * Disconnect from the event registry
+   */
+  void xbacklight_module::teardown() {
+    m_connection.detach_sink(this, 1);
+  }
+
   /**
    * Handler for XCB_RANDR_NOTIFY events
    */