Parametric remote control cover + multi stand

##[18 DEC 2020 - V 1.1]
- Changed support vertical angle from 20° to 15° since it could cause interference with longer remote controls.
- Moved some internal variables definition to HIDDEN section, since Thingiverse Customizer was showing them.
- Fix on some internal variables using raw parameters instead of "sanitized" ones.

##[17 DEC 2020 - V 1.0]
This is a *fully parametric* multi-RC holder stand (TV or AC, or whatever, not RC for drones...)

Summary:

- Custom remote size
- Up to 5 remotes in a single tailored stand
- Custom remote cover attachment (magnets/recess)

You can define up to 5 remote control sizes and you'll get a custom cover and a single-remote or multi-remote stand. The stand is designed to adapt to the different remote sizes you define.

The cover then can be attached to the stand and removed when needed, so that if you have multiple stands you can place the same cover in another stand.

You can choose if you want to attach the cover to the stand