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

     1

{

     2

    "ID": "wamptest", 

     3

    "active": true, 

     4

    "protocolOptions": {

     5

        "autoPingInterval": 60, 

     6

        "autoPingTimeout": 20

     7

    }, 

     8

    "realm": "Automation", 

     9

    "url": "ws://127.0.0.1:8888"

    10

}