Improved navigation between commits affecting a specific resource in a git repo (BB-10431)

To view the state of a specific resource throughout the history of commits that affected it in a git repo, currently bitbucket only offers a navigable drop-down menu of said applicable commits, reloading the view every time a new one is selected.

This accomplishes the goal of showing the various states of the resource throughout its development, but in a rather cumbersome way; e.g. if the resource is affected by a very large number of commits, the simple task of browsing between a few adjacent ones far off from the "head" revision becomes rather annoying: you have to scroll all the way down in the menu every single time you want to select a new commit, which is a clumsy operation at best.

A much better way to accomplish the same task would be a pair of "back" and "forward" buttons/links that would simply take the resource one commit back or forth, respectively, from the one it's currently being displayed at, much in a similar way to how Trac does it in its subversion source browser, e.g.:

http://trac.macports.org/browser/trunk/Makefile\\
(mind the "Previous Revision" and "Next Revision" links on the upper-right corner)

These new button/links wouldn't have to replace the commits menu entirely. They could perfectly sit to either side of it, or both to a single side, simply to offer an easier navigation approach to adjacent commits for a resource.