Avoid panics

[jsign]

Do a full-scan of the repository to avoid explicit panics. Even though we usually use them in cases where critical invariants must hold, panicking is very aggressive for at least a graceful shutdown, even in non-recoverable errors.

Also, scan for dependencies (e.g: go-ipa) for the same.

We can do this getting closer to a stable implementation, and definitely before getting close to being fully integrated in geth since it can result in breaking some APIs returning errors instead of panicking.

cc @gballet

[gballet]

Yeah that's too many

~/s/go-verkle (master)> grep -r panic * | wc -l
29