Summary:
This shows the commits list only (Actual `git diff` will show up at a later date).
The inputs are left as text-fields, to allow the form to accept anything that can be resolved. The form is GET, to allow sharing URIs.
The conduit method response array is compatible with that of `diffusion.historyquery`, to make it easy to build
the "history" table.
The hardest part here was, of course, Naming. I think "from" and "onto" are unconfusing, and I'm fairly confident that the "to merge"
instructions are in sync with the actual content of the page.
Test Plan: Look at several "compare" views, with various values of "from" and "onto".
Reviewers: #blessed_reviewers!, epriestley
Subscribers: caov297, 20after4, Sam2304, reardencode, baileyb, chad, Korvin
Maniphest Tasks: T929
Differential Revision: https://secure.phabricator.com/D15330
