Bug 834707 - Disable SOWs for remote XUL domains. r=bz

We have to do this if we want to proceed with eliminating SOWs entirely. Given
the other restrictions around remote XUL, I don't think this is a problem.

Note that we shouldn't need any special handling in the wrapper reparenting
paths, because those all depend on whether a SOW was there already. So that
would only be an issue if it were possible to adoptNode from a non-remote-XUL
domain into a remote-XUL domain, which thankfully can't happen.
Bug 834707 - Kill dynamic SOWs. r=gabor

Now that XBL scopes are here to stay (no more pref), we can remove all the
machinery that makes SOWs dynamic. We still need SOWs until bug 825392 is
fixed, but they can now be totally opaque.

One side effect of this patch is that, due to our usage of Opaque, we now
allow CALL on SOWs. But this shouldn't be a problem, because SOWs are used
for anonymous elements which are not callable (and we probably wouldn't mind
it even if they were).