Smart Spool Holder

**UPDATE**
I've added a new rev. B: check below for improvements.

I have searched and tested many spool holders, but none actually fit my requirements so I made my own using designs I've found here as a reference, in particular:

* [this design](https://www.thingiverse.com/thing:1319713) from [ali55](https://www.thingiverse.com/ali55)
* [this deisgn](https://www.thingiverse.com/thing:1725851) made by [steveyum](https://www.thingiverse.com/steveyum)

This spool holder is meant to stand