This PR contains multiple fixes. The most important of which is:
* Prevent hang in git cat-file if the repository is not a valid repository
Unfortunately it appears that if git cat-file is run in an invalid
repository it will hang until stdin is closed. This will result in
deadlocked /pulls pages and dangling git cat-file calls if a broken
repository is tried to be reviewed or pulls exists for a broken
repository.
Fix #14734
Fix #9271
Fix #16113
Otherwise there are a few small other fixes included which this PR was initially intending to fix:
* Fix panic on partial compares due to missing PullRequestWorkInProgressPrefixes
* Fix links on pulls pages due to regression from #17551 - by making most /issues routes match /pulls too - Fix #17983
* Fix links on feeds pages due to another regression from #17551 but also fix issue with syncing tags - Fix #17943
* Add missing locale entries for oauth group claims
* Prevent NPEs if ColorFormat is called on nil users, repos or teams.
* Some refactors related repository model
* Move more methods out of repository
* Move repository into models/repo
* Fix test
* Fix test
* some improvements
* Remove unnecessary function
