feat($compile): support modifying the DOM structure in postlink fn

Support modifying the DOM structure in the post link function of a directive
by creating a defensive copy of the node list, as opposed to a live DOM list.
This is useful for directives to actually replace their entire DOM fragment,
e.g. with the HTML fragment generated by a 3rd party component (Closure, Bootstrap ...).
Fix the indentation of the compileNodes function (was one too little).