Fix verification messages

[JensNexus]

The verifier reports back the time to verify, but not wether the proof was accepted or not. The verifier should give an explicit accept or reject message.
I tried using the Cargo.toml file as "proof". The verifier panicked. It would be nicer to reject the proof with an error message.

[slumber]

The panic comes from ark-serialize. We can try to catch_unwind, but the message would still be ugly

[MrHIB]

same problem