Improve main menu

Add a few improvements to the menu script:

• Sort apps by their name, not filesystem path (Credit goes to @fleur!)
• Show a loading screen immediately to be more responsive (Requested by @schneider)
• Add a list of favorite apps which are shown at the very top
• Add a USB Storage entry that opens the filesystem via USB (Thanks to @swym for the base-work below this!)

Supersedes !336 (closed) (includes that change in 0322ab41).