Make panics human-friendly

[Arkanosis]

There aren't many panics left, hopefully, but given there're still a few unwrap in some places, it'd be better to catch them to help the end user to report them.

One option would be to use human-panic for this.

What's needed:

• error message
• full stack + version in a file
• bug report URI (preferably bamrescue.arkanosis.net/report_bug which would redirect to GitHub issues, with the ability to change the actual target at any time)