Option to disable command verification

This change adds the option to disable command verification.

Rationale: Both the .yaml file AND the official Onkyo documentation lag behind current models (for example, latest 1.26 ISCP doc does not yet cover the NR535). For unknown models, NO high level commands are then available. By disabling this verification, it's then possible to send commands anyway. The worst that can happen is that the AVR sends an error. get_commands() etc. are unchanged.

Default behavior is verify_commands=true, so unchanged to previous behavior.