Move desktop notifications to its own header

We'll need to use this from the chainloader.

src/plugin/bridges/common.h

@@ -26,12 +26,10 @@
 #include <version.h>
 
 #include "../../common/configuration.h"
+#include "../../common/notifications.h"
 #include "../../common/utils.h"
 #include "../host-process.h"
 
-// FIXME: This should be passed as an argument instead
-#include "../../common/linking.h"
-
 /**
  * If the amount of lockable memory is below this, then we'll warn about it
  * during startup. Otherwise we may run into issues when mapping shared memory