Re-split the transclusion dialog

We used to have two dialogs; a complex one, and a subclass that dumbed it
down - this was rubbish.

Then we merged them together - this was a'ight.

Now we have two dialogs again; a simple one, and a subclass that fancies
it up a bit - this is wicked keen broham.

Change-Id: I4b2ba31bed5c4f80940623702d635cacd19e0a66