The code setting a default for MenuView's element ID didn't work

correctly. The approach failed to set an ID when the default was an

empty string, and also tried to set the ID too late (initialize() is

called after the element is created).
We now set the ID more explicitly during initialize() and during

render.

Verified that a MenuView used in Review Board had an automatic ID

set, and that MenuViews with an ID didn't have it replaced.