Can you figure out what this strange method does?

Summary:
Add the ability to intercept interWidgets calls in a renderer.
This allows parents of a renderer, such as the group widget,
to customize how interWidget communication happens within
their renderers.

The group widget here forwards interwidget communication
to the outer renderer if no matching widgets are found
inside the group widget.

Test Plan:
Visit [this
item](http://localhost:9000/test.html#content=%7B%22question%22%3A%7B%22content%22%3A%22%5B%5B%E2%98%83%20passage%202%5D%5D%5Cn%5Cn%5B%5B%E2%98%83%20group%201%5D%5D%22%2C%22images%22%3A%7B%22https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2Fda8df81c78b22f5c69d477d8eabfb583968eaf84.png%22%3A%7B%22width%22%3A400%2C%22height%22%3A70%7D%2C%22https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2Fb59fc02ca1aae800977b8793ed22f647a1aa75ee.png%22%3A%7B%22width%22%3A425%2C%22height%22%3A150%7D%7D%2C%22widgets%22%3A%7B%22passage%202%22%3A%7B%22type%22%3A%22passage%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22passageTitle%22%3A%22%22%2C%22passageText%22%3A%22Lorem%20Ipsum%20is%20%7B%7B__simply%20dummy%20text%20of%20the%20printing%20and%20typesetting%20industry.%20Lorem%20Ipsum%20has%20been%20the%20industry%27s%20standard%20dummy%20text%20ever%20since%20the%201500s__%7D%7D%2C%20when%20an%20unknown%20printer%20took%20a%20galley%20of%20type%20and%20scrambled%20it%20to%20make%20a%20type%20specimen%20book.%20It%20has%20survived%20not%20only%20five%20centuries%2C%20but%20also%20the%20leap%20into%20electronic%20typesetting%2C%20remaining%20essentially%20unchanged.%20It%20was%20popularised%20in%20the%201960s%20with%20the%20release%20of%20Letraset%20sheets%20containing%20Lorem%20Ipsum%20passages%2C%20and%20more%20recently%20with%20desktop%20publishing%20software%20like%20Aldus%20PageMaker%20including%20versions%20of%20Lorem%20Ipsum.%22%2C%22footnotes%22%3A%22%22%2C%22showLineNumbers%22%3Atrue%7D%2C%22version%22%3A%7B%22major%22%3A0%2C%22minor%22%3A0%7D%7D%2C%22group%201%22%3A%7B%22type%22%3A%22group%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22content%22%3A%22%5B%5B%E2%98%83%20passage-ref%201%5D%5D%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%22passage-ref%201%22%3A%7B%22type%22%3A%22passage-ref%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22passageNumber%22%3A2%2C%22referenceNumber%22%3A1%7D%2C%22version%22%3A%7B%22major%22%3A0%2C%22minor%22%3A0%7D%7D%7D%7D%2C%22version%22%3A%7B%22major%22%3A0%2C%22minor%22%3A0%7D%7D%7D%7D%2C%22answerArea%22%3A%7B%22type%22%3A%22multiple%22%2C%22options%22%3A%7B%22content%22%3A%22%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%7D%7D%2C%22calculator%22%3Afalse%7D%2C%22itemDataVersion%22%3A%7B%22major%22%3A0%2C%22minor%22%3A1%7D%2C%22hints%22%3A%5B%5D%7D),
which has a passage, a group, and a passage-ref inside the group,
and see that the passage-ref is working (which requires interWidgets
access to the passage widget).

Reviewers: alex

Reviewed By: alex

Subscribers: dylan

Differential Revision: http://phabricator.khanacademy.org/D13765