Improve the contribution templates to enforce standard behavior

[krestenlaust]

Right now, people seem to disregard the contribution templates, like I've done here (removing the template and writing a wall of text). Adding more firm language and a disclaimer in the beginning that tells people to leave in the headers. There's a ton of enhancement suggestions but it's hard to recognize an issue when they're all walls of text.

Replacing the comments in the templates with "Replace this text" or similar, could also nudge people towards not removing everything.

[Nutomic]

Contributions welcome. A yml template like this one would be ideal as it allows specifying mandatory fields.

[krestenlaust]

This is an awesome change, it's much better now!