Add launcher.conf.json option speaker option (DOS fix)

[RetiredWizard]

This adds an option to the launcher.conf.json file to send the boot audio to the speaker instead of the headphones.

{
    "sound": "speaker"
}

I'm thinking this would be a useful modification to make to at least the larsio music paint program, especially since the Fruit Jam ships with a speaker. I'll work on a learning system PR for that.

I also noticed an issue when the Fruit Jam is not connected to a host computer and a local USB keyboard is being used. When PyDOS (and possibly any app) starts there seems to be some data in the serial buffer which gets interpreted as keyboard input. This was causing the initial PyDOS prompt asking for read-only files system reboot to get bypassed. I modified the prompt so if one of the two required responses isn't entered, an invalid entry message is displayed and the user is re-prompted.

[FoamyGuy]

Nice, Thank you!