GitLab reorganization stuffs

This updates the contributing doc slightly to update it to the new labels and adds a few more explanations of other labels. It also uses the ~"label" syntax which GitLab will then show as a special link (example: StageDenied). The file can be previewed on GitLab here with all the labels created. I'm not entirely sure if the wording is proper but it gives us somewhere to start.

I also created an issue template for bug reports. I'm not sure if there's more information that could go under the Platform section that could be useful, maybe browser extensions?