Make the index.html file functional

[zelon88]

• Add "narrow" GUI for small screen devices.
• Make index.html have three options, configurable in config.php.
• Option 1 is to redirect all users to convertGui1.php and let the core use default settings.
• Option 2 is to redirect all users to convertGui1.php based on screen size only.
• Option 3 is to prompt the user for options that are allowed (color, gui, minimal UI, language, high visibility) or to automatically pre-processes these from GET input.