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/WatchFaceDigital.h

@@ -4,8 +4,8 @@
 #include <chrono>
 #include <cstdint>
 #include <memory>
-#include "Screen.h"
-#include "ScreenList.h"
+#include "displayapp/screens/Screen.h"
+#include "displayapp/screens/ScreenList.h"
 #include "components/datetime/DateTimeController.h"
 
 namespace Pinetime {