GitHub: ask for more info in issue templates

[JohannesGaessler]

This PR updates the issue templates and adds more fields to ask for potentially useful debugging information (since I find that a lot of the time I end up asking the same questions when I am the first responder to issues). A live version of the templates is on my fork.

[ngxson]

I think we should refactor the category for issues too, ref: #8097

[slaren]

For me the severity tag is completely useless. People reporting bugs should not make that decision anyway.

[JohannesGaessler]

I pushed refactored templates for compilation, model evaluation, and miscellaneous bugs. I don't know what information would be needed for e.g. a bug report concerning the server and would ask someone more knowledgeable than me to create such a template instead.

[ExtReMLapin]

For me the severity tag is completely useless. People reporting bugs should not make that decision anyway.

Don't forget my™ problem is always more important than your™ problem.

[ngxson]

I don't know what information would be needed for e.g. a bug report concerning the server and would ask someone more knowledgeable than me to create such a template instead.

In most cases, having the log output is already enough to pinpoint the problem.

[ngxson]

Looks good now, thanks. I think we can already merge this to see how it goes, and improve from this in the future.