3.9.1-BETA-3476 Firmware for MK3, MK3S, MK2.5 and MK2.5S

This is a Beta firmware to test some potential fixes. This is a replacement for v3.9.1-BETA-3464

• LA1.5 fix, please see and report back here Report: LA1.5 fix
• Altfan menu

NEVER let the printer unattended using this firmware