More PR / issue tags.

[yuri-kiss]

We REALLY need more PR / issue tags to help organize this mess of a system (no offence).

(Maintainers just use the edit button and add to my issue down below)

Tags and their purposes; suggestions in no particular order except when we came up with them.
pr: indepth review required : This PR requires a deeper review and may take longer than expected.
pr: merge conflicts: This PR has merge conflicts and should NOT be approved.
pr: stale: This PR is stale and has warrent to be closed in due time.
pr: unstable patches: This means unstable patches were used.
pr/issue: duplicate: Self explanitory.