Add a toolbar for merge/close/aprove when scrolling a PR

Add a toolbar that only shows when you start scrolling a PR with the buttons merge, close, aprove, back to top, so that when reviewing large PRs you can simply take any actions there without having to scroll 50000 lines up to press the buttons. (maybe some other options would be cool, but those 3 are the buttons I feel lacking). Also the button "ignore white spaces" should be there too, since when you select in one file it will be applied to all anyway.