Improvement: Track the homing status of the selector

[eamars]

I came across this idea when working on my ERCF code. Hopefully my proposed solution could improve the overall robustness of the selector motion.

The idea is to mimic the current printer design, that is, when the axis is not homed then it should'nt move. In this case, the selector shouldn't move if its location is unknown. This can be achieved by using an variable to track the current position, say the _current_tool. The variable got reset on

• Printer connect
• M18/M84 command is issued.
• ERCF_MOTORS_OFF is called.

The selector move command shall use this variable to determine whether the selector is homed or whether it need to move, instead of "attempting to move" causing extra variations.

Please let me know if you have any comment on this.