Update includes to to be relative to src directory

Don't use relative imports like `../foo.h` as those depend on the
relative position of both files. Rather than that use imports relative
to the `src` directory, which explicitly is part of the include
directories.

src/displayapp/screens/Alarm.h

@@ -17,9 +17,9 @@
 */
 #pragma once
 
-#include "Screen.h"
+#include "displayapp/screens/Screen.h"
 #include "systemtask/SystemTask.h"
-#include "../LittleVgl.h"
+#include "displayapp/LittleVgl.h"
 #include "components/alarm/AlarmController.h"
 
 namespace Pinetime {