Add possibility to add/edit spool length about spoolman

[Donkie]

You mean you want to be able to specify a "used spool length" (in mm) instead of "used spool weight" when creating a new spool?

[Hesi-Re]

Yes. "Used spool length" and "available spool length". For example, when creating new spool it's helpful to specify de total spool length (ex: 1000g -> 335,28m), so when printing it subtracts the used filament length, not only the weight.

[Hesi-Re]

If I cut 2 m of the filament, it would be nice to subtract it to the spool

[Donkie]

That feature is already requested in #30

Hello and thank you for Spoolman!
The length option is great, would it be possible to choose mm, cm or metre?