Introduce `--verbose` option for `fiora-predict` script

[janlisec]

Consider an option to mute print statements generated in the script.

Bests [jan]

[janlisec]

@ch4perone you may close this issue. I call fiora-predict within the R package fioRa using system2(). I implemented a verbose option there which sets stdout=NULL thus avoiding any messages being written to the R console.