MQTT: add JSON payload corresponding to IEC Structured types

- uses https://github.com/cesanta/frozen
- frozen.c is added as a resulting c file in generat_C (fix toolchain_gcc.py as it was breaking dependency checking)
- structured types are converted to C #define, in turn generating json_scanf and json_printf statements

#!/bin/bash

set -e

echo "Building docker image"
cp -f ../../../requirements.txt requirements.txt
docker build \
    --build-arg UID=$(id -u) \
    --build-arg GID=$(id -g) \
    -t beremiz_sikuli .