Consider restricting compilations to include only scenes listed in the scene_list

Currently CSIDE includes _all_ .txt files in the project directory for compilation, both for exporting and running games. It's known that CoG often likes scenes to be explicitly listed in the startup.txt's scene_list, and this is actually required by the standalone compile.html (although in this case it is for purely technical reasons). Thus it would make sense to adhere to this 'standard' and encourage people to explicitly list their active scenes in the scene_list, in order to include it any compilation. This would also have the added advantage of allowing notes and copies of files to be included in the project directory, without fear of them being accidentally included in any compilation (which can also cause compilation failures, if the .txt files contain unsupported characters).

On the downside, this does somewhat raise the barrier (if only slightly) to getting started with CSIDE, and will somewhat slow down the process of adding new scenes. Additionally, although the scene_list seems like a preferred notion, ChoiceScript itself does not forbid loading scenes not listed in scene_list (via goto_scene).

Finally, because we have been allowing this to date, there's a concern that changing this now will require some extensive scene_list gardening of user's current projects.