Add better system for expected crashes

[SnowyCoder]

A user reported that when the plugin crashed he couldn't figure out what was the problem, we developers had trouble checking it too.
Later on we discovered it was because the economy plugin was missing but that's not the point, we need a better way to tell the user why the plugin crashed and how to solve this.
A way to fix it would be to create an ExpectedCrash or something similar that can give some suggestions that help the user to fix the problem.
A little enhancement that is now present in the master branch is to save the trace to a file (so the console isn't filled with debug info) and to delimit the error making it clear that it is a real crash.

[SnowyCoder]

For reference see the rust compiler's errors, they're compact, clear and also give some pointers that explain how the error might be resolved.
It's impossible to provide a system like that for any kind of error but we could apply something similar in some sub-systems (config parsing and some exceptions that are quite easy to get, like missing plugins)