add debian package for bmx7

[aparcar]

[axn]

The hard dependencies are mbedtls and zlib Depending on selected plugins also: libjson-c for json plugin uci (https://openwrt.org/de/doc/uci) for uci-config plugin Unfortunately, as far as I know, there is no debian package for the latter yet.

This ticket is related with bmx6 debian-package request issue: https://github.com/bmx-routing/bmx6/issues/13