While the merge editor shows users can handle merge conflicts outside of it, e.g on the console via `git add <FILE>`. The merge editor should have this graceful and step one is to hide the "Accept Merge" command when the file isn't conflicting anymore
* Adds a git-context key that contains all resource-uri-strings under conflict
* Enable/placement of the Accept Merge command is driven by that
* some merge editor context key sugar