Update HTML5 demo

[johnwdubois]

1. Update the HTML5/demo/itch.io release, bringing it into the main line of development for Windows and Mac (as much as possible).
2. Isolate and minimize any necessary differences in code & functionality between HTML5 and PC/Mac, to simplify future maintenance of HTML5 releases.
3. In the long run, seek native GML solutions for web, for:
   • file handling
   • audio playback

[terrydubois]

Still left to do:

• Add REZ files 1-10
• Use Noto Sans fonts with large range (try CJK)
• Disable file menu options (save, media, etc)
• Add other locale files
• Address Ctrl+Click for Mac browser
• Make website buttons open in new tab
• Disable "check for updates"