[Request] Support for Debian netinstall image

[kord1e]

Currently, the following Debian images are supported:

• Live, which is not good if one wants to use the traditional installer (the Calamares installer in the live image is actually really bad)

• mini.iso, which is not easy to find, and Debian doesn't seem to provide checksums or signatures to verify its integrity which is a must for many users

Thus it would be very nice if the netinstall image could be supported.

[ngaro]

It's fixed in CIBU and should also work in GLIM . Get the file here and put it in your grub2 dir.

[ngaro]

I made an error but it's fixed now both in GLIM and CIBU. (the grub.cfg also needed changes)
See what this pr does and make the same changes or wait until the PR is merged if you are going to use GLIM. (Which I would recommend for now. My CIBU is still in heavy development)

[mmercurio]

Nice job, @ngaro! This works well.