refactor($compile): automatically append end comment nodes to all element-transclusion templates

Previously we would do it manually in all of our structural directives.

BREAKING CHANGE: element-transcluded directives now have an extra comment automatically appended to their cloned DOM

This comment is usually needed to keep track the end boundary in the event child directives modify the root node(s).
If not used for this purpose it can be safely ignored.
refactor(jqLite): simplify jqLiteAddNodes when multiple nodes are being added

This branch is not as hot as the single node branch and the slice that we need for old webkit/phantom makes for loop preferable.
WIP: remove todo

the comment was moved to template but we can't clone the template via document fragment because
for 1-5 elements document fragment is only an extra overhead. It only starts to make things faster
when we have 10 or more root elements to clone and append