[messages] add INFO_MSG and with printing to GCS console

Intention is to be able to send info/debug messages via telemetry and see them in messages and the GCS console.
E.g.
``` c
const char *str = "test foo";
DOWNLINK_SEND_INFO_MSG(DefaultChannel, DefaultDevice, strlen(str), str);
```

Added a string_of_chars function to pretty print char arrays as strings so you get `test` instead of `|t,e,s,t|` in the GCS console and messages app.
(My OCaml fu is not very strong, so how that is done is probably not the nicest way).

Bind to the INFO_MSG in live and log_and_say to console.