TOB-DQK-007 remove panics

[MarioDfinity]

I removed the (panic|unwrap|expect)s from the project on bad user inputs and similar errors that are expected to happen and should be reported with a human friendly message. Some of my changes are redundant, e.g. the unwrap on opts that get also validated by validators, but the new code is not much more than unwrapping.

I also added some tests in main.rs that helped me validating my changes to that file.

[roman-kashitsyn]

Great work! I think we can improve it further by using context or with_context feature of anyhow as much as possible. These functions wrap the errors to form a chain, which makes it possible for us to be more creative and helpful when we display the error.

[MarioDfinity]

The build is going to fail because files are not importing anyhow::Context. I'll fix it myself in a moment.

[MarioDfinity]

@roman-kashitsyn I've changed most of the code to use context instead of map_err when it makes sense. map_err is now used only to wrap an error not supported by anyhow inside an anyhow error. Please have a look again.