Add support for D-Link COVR-X1860

I've set up a cron job (and run a couple of manual test builds) which creates nightly builds and makes the bin/target folder available on my server:

The source code can be found here:

The firmware images can be found in the targets folder. The firmware is set up to automatically fetch the core packages (aka. kmods) from my server and I'll make sure to keep each build around for at least 14 days, meaning installation of kernel modules will be possible for at least 14 days.

The base image contains a few extra packages that I wanted for my system and didn't want to install manually (especially after firmware upgrades), namely miniupnpd and its LuCi module, DAWN + LuCi, batman-adv + LuCi, etherwake + LuCi, vnstat2 + LuCi, the Material theme for LuCi, and wpad-mesh-mbedtls instead of the basic package. If this is too many default packages, let me know and I'll get rid of a few. Alternatively you can also disable the unused services after flashing.

Let me know if anything goes wrong.