Jump to modified file with Enter key in "Git Diff" view

With this patch we are able to use the Enter key in an inserted/eliminated line of "Git Diff" view to jump directly to that location of the modified file.

Part of this feature was requested in [issue 104](https://github.com/kemayo/sublime-text-2-git/issues/104), but instead of using the mouse click we've to press the Enter key when the cursor is over a inserted/eliminated line.