Improve CLI and runtime error messages

[KristianKarl-zz]

Improve the feedback from GW to a user.

[nbdnnm]

Is there a list of what to be improved?
I try to understand should I rise few things which I have noticed or it is already known and planned to be fixed?

[KristianKarl-zz]

The idea here is to ensure that gw is providing good enough error messages and help when using the tool.
A user should not get stuck, just because we don't provide good information about some problem.

Like, if the user tries to load model(s) in a file, and types the wrong path to that file. GW should tell the user exactly that.

Long stack traces are in most cases not helpful to a normal user. Too much noise. The information should be short, sweet and to the point.