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/lv_pinetime_theme.c

@@ -6,7 +6,7 @@
 /*********************
  *      INCLUDES
  *********************/
-#include "lv_pinetime_theme.h"
+#include "displayapp/lv_pinetime_theme.h"
 
 /*********************
  *      DEFINES