Summary:
Added a dropdown menu button and the keyboard shortcut 'h' to the
web diff view. These hide or show the annotated code display.
Test Plan:
Viewed an example diff that changed a large number of source files
and played around with keyboard shortcuts. Everything seemed to
work as expected.
Reviewers: nh, epriestley
Reviewed By: epriestley
CC: aran, epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D2714
