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/Paddle.h

@@ -2,7 +2,7 @@
 
 #include <lvgl/lvgl.h>
 #include <cstdint>
-#include "Screen.h"
+#include "displayapp/screens/Screen.h"
 
 namespace Pinetime {
   namespace Components {