Add keyboard navigation to the review tool

[sdefresne]

It would be good to have keyboard navigation to go to the next / previous modified chunk / file in the review tool so that we can easily review a change list.

The keyboard navigation must expand the diff when navigating to it, and if moving between files, it should fold the previous file diff.

[esprehn]

Press the "e" key to expand all diffs, then just scroll with your trackpad. Jumping between chunks doesn't really make sense in the new tool but I'll consider it.