Improve the commitdiff.

Same as PR-225, but against gitblit:develop.

Width of the line number columns reduced to 2px padding and 3em width. On my screen the three columns (two line numbers and +/-) are 95px, vs. the two line number columns at dev.gitblit at 82px.

Sorry for the duplicate PR, but GitHub didn't let me rewrite the original PR (which was based on master). I just hope I didn't mess up somewhere in this rebase confusion.
Of course one would need to adapt also CommitDiffPage and ComparePage to use `'n' + entry.objectId` for the fragment (that's two one-liner changes in each page). As far as I see those are the only places where page-internal links to the file diffs are generated.

When I wrote "in both places" I meant in those two pages, plus here in GitBlitDiffFormatter for the ids. I've actually tried this locally, and it works nicely, and simply side-steps all problems with strange characters in paths.