Improvements to Diff Viewer

[20wildmanj]

Request from 122 (Iliano):

the submission diff viewer has been a significant time saver when investigating possible AIVs, not to speak about the improved accuracy. A couple suggestions:

• Could you mark clearly which side is which version? Right now it's not obvious and once I figure it out I forget the next time I need to use it.
• An obvious extension would be to give us a way to compare the current student/file/version with the same file of an arbitrary student and version. You could for example keep the default behavior the same, but provide a dropdown menus for student and version.

[KesterTan]

Provide a "combined diff" so that we can explore the differences in all submitted files at once. Right now, if a student makes 10 submissions with 5 files each, I have to examine 50 diffs (actually, 45). With a combined diff, this goes down to 9 -- much more efficient.

In the "File Outline" pane, add a "Combined" item where all the files are stitched together like in MOSS (with markers so that make it clear when one starts and the next begins).