The showSendEmail attribute was being passed to ChangeBoxView,

ReviewBoxView, and InitialStatusUpdatesBoxView individually, and then

being forwarded on to other views. This state is really global, and not

per-box, and with some of the upcoming work, it ends up being

increasingly annoying to pass this state individually through the views.
The attribute is now part of ReviewRequestEditor, which gets passed to

these views instead. Some of the views already take this editor, and

more will need it with some upcoming work anyway. Some of the new

statements will even be rewritten in the upcoming change. This just

simplifies the options/attributes needed by views and lays the ground

work for those changes.

JavaScript unit tests passed.
Tested the draft banner for review request updates, draft reviews on a

review request, draft replies on reviews, draft replies on initial status

updates, and draft replies on changedesc-associated status updates. These

were all tested with and without e-mail enabled (which is what the

showSendEmail flag is bound to).