Opengb

Added
- API method set_extrude_override
- API event extrude_override_change
- API method set_speed_override
- API event speed_override_change
- API method set_fan_speed
- API event fan_speed_change

Added
- Metadata parameters to gcode files
- Thumbnail parameter to gcode files

Fixed
- Reconnect to printer when USB unplugged during execution
- Reset printer when hardware powered off during execution

Fixed
- Frontend directory missing from package

Added
- Enable/disable steppers functions
- UI improvements

Fixed
- Distinguish between nozzle 1 and 2 temps when heating for prints