Patch Set 2: I would prefer that you didn't submit this

looks quite good, but some things could still be improved (your choice if you do this in this change or a later one):
- can't open compare view on untracked file but on deleted file, to not surprise users this should be also possible on untracked files
- staging view doesn't recognize if a new (hence untracked file) is created or an existing one is modified and saved
- I think by default compare view should be reused so that you don't end up with lots of these views when inspecting the current status. There could be a toggle to pin compare view so that subsequent double click would add a new compare view for the next file.
- when compare view is already open and not pinned selecting another file in staging view could automatically update the compare view. This would save one click per file navigation.
- staging through drag&drop doesn't yet work (don't know if it should already)