Error Handling

[mustermeiszer]

Currently, the whole lib is basically unwrapping everywhere most of the time.

In the future the lib should define its own error enum that wraps ALL underlying substrate errors into respective variants and also exposes a set of fudge specific errors.

Tasks

• Encapsulate lower level errors in enum and define error enum for lib
• Handle every unwrap by using errors and results instead

[mustermeiszer]

Done in #60