Scenes Demo Application Tutorial

This is an exampe similar to Basic_Scenes but with the files broken out into separate .c and .h files.

The static keyword is used on functions that do not need to be visible beyond their own .c file.
#pragma once is used to prevent the header file from being imported multiple times.
We don't use the typical typedef struct App App pattern in basic_scenes_split.h because the various scenes access properties of the App object.