Move the end-of-spool remainder of filament into another, dedicated spool

[UltimaCarbo]

First of all, Hi! A huge thanks for creating this, it was exactly what I was looking for!
Second, please forgive me if I am not doing something right, this is my first time posting on github and I really don't know what I am doing :) So I hope I am in the right place

Is your feature request related to a problem? Please describe.
What I do when a spool is about to run out, I weld the remainder of the filament onto a dedicated spool I keep for this exact purpose. I then use that multi-coloured tail-end spool for test prints or for things I don't care how they look. Like this: https://ibb.co/z8Zk9nP
That reduces waste and I get more bang for my buck for the filament.

Describe the solution you'd like
It would be great if there was a option to declare a spool as an tail-end-collection-spool (not sure what to call this). Then, it would be great if one could migrate the remainder of a spool to that dedicated tail-end-collection-spool (or any other spool, for that matter).

At the same time, I would appreciate if one could select multiple colours for the filament.

EDIT: Also, it would be helpful if we could enter remaining or used filament amounts in meters, not just in weights. But that may be a separate feature request :)

Describe alternatives you've considered
An alternative, of course, is to do it manually, which I am doing at the moment.

I am probably the only one interested in this, but thanks anyway!