view.Writer should deeply unlink attribute elements from their groups when they are removed

[scofalik]

Currently, view.AttributeElements which have id property set are linked together in view.Writer in so called "clone groups". All elements with the same id that are still in document tree are inside the group.

When elements are removed from the document tree, they are removed from the groups. However, the function that does so is not looking recursively for the elements.

That means that in following scenarios it will fail to remove <span class="a">:

<p>f[oo</p>
<p>b<span class="a"a</span>r</p>
<p>b]az</p>

[scofalik]

There might be a similar problem with adding elements to groups.

[scofalik]

Additionally, I noticed that the attribute elements might be added to clone groups if they are added in a DocumentFragment (outside of document tree) which is wrong too.