Publish firmware selector

[Paul Spooren]

Hi all,

The firmware selector is a simple search form where end-users can find
firmware images for devices. It's based on Moritz Warnings great work,
featuring Petr and Richs code and comments.

A staging version can be found here:
https://firmware-selector.staging.openwrt.org/

Moritz and me concluded that the selector is ready for some action,
which means it would be deployed at the following address:
https://firmware-selector.openwrt.org

This should be combined with a newsletter announcement, a forum post and
link in the download section on openwrt.org.

Please test the selector and share objections against a release.

Kind regards,
Paul