New build script

[pktpls]

New build script in the same simple style as build.sh in falter-packages. It supports everything that the old build_falter script supports:

• build all devices of a target, or a specific device
• build tunneldigger/notunnel/backbone variants
• snapshot, 1.4.0, 1.3.0, 1.2.3, testbuildbot branches
• custom falter package feed, local or http
• device quirks via OpenWrt table of hardware (low ram, low flash, wave1 non-CT driver)
• version info in /etc/freifunk_release
• custom login banner, luci favicon, luci footer

Two more small things missing: 1) more detailed usage help text, 2) custom imagebuilder option.

Will squash the commits before merging.

[pktpls]

This PR now also includes:

• the same linter and github actions work as in github: make lint, formalities falter-packages#432
• rework of vm.sh with support for rebooting after completing the wizard
• remove kmod-dwmac-intel which is currently broken in OpenWrt upstream

[Akira25]

Thank you very much for the rewrite! I'm sorry, that I wasn't able to look on it before, but looks really neat.