Better suppression of multiple M114 commands
Don't send G90 if it has already been sent
issue: MatterHackers/MCCentral#5227
Can't unload T1
issue: MatterHackers/MCCentral#5219
'Unload filament' extrudes filament indefinitely.
Only build a movement string for the values we know the position of
initialize unknown positions to Unknown (rather than Zero)
Added get to check for fully known position
issue: MatterHackers/MCCentral#4681
Export making M114 assumptions about Z