Improve detection for the Prusa version

[jukebox42]

Improve detection for the Prusa version by adding additional checkpoints and simplifying how it's pulled.

New Features:

• N/A

Bug Fixes:

• Fix the nav status for MK4s
• Rewrite firmware checking to have a backup. machine type seems not to trigger every time
• Default the printer to an MK3 if we haven't detected the printer and the user starts printing (future versions will give you a setting to override)
• Update the the initial version detection to trigger an event, gets the MK version to the UI quicker

Internals:

• Ditch M863.6 MMU detection, it wasn't actually telling you the MMU was ok. We should assume all users have an MMU
• Clean up the gcode file and remove it, it was an artifact from when I was trying to get single print to work for the MK4