It's been passed in for a while, but nothing ever used it. As we know
some browsers don't like it when we create elements in the wrong
document, and this ensures we always use the correct document for
createElement().
Change-Id: Ia3d2fabe0516956105ad2b5625ed2f76c015c26e
ve.dm.Model is now the common base class for these three. ve.dm.Node
inherited from ve.Node before, so it now uses it as a mixin instead.
This required changing ve.Node's usage of ve.EventEmitter from
inhertiance to a mixin as well, because inherited methods apparently
don't get mixed in correctly.
* Change annotation terminology from linmodAnnotation to element for
consistency with Node, MetaItem and Model
* Reimplement getClonedElement() in Node for .internal treatment
Change-Id: Ifd3922af23557c0b0f8984d36b31c8a1e2ec497e
