This patch removes support for mozapp iframes, leaving support for
mozbrowser iframes intact. Some of the code has been rewritten in order
to phrase things in terms of mozbrowser only, as opposed to mozbrowser
or app. In some places, code that was only useful with apps has been
completely removed, so that the APIs consumed can also be removed. In
some places where the notion of appId was bleeding out of this API, now
we use NO_APP_ID. Other notions of appId which were restricted to this
API have been removed.
