feat(ngRepeat): use block separator comments

Issue: multi-elements ng-repeat (ng-repeat-start, ng-repeat-end) can contain elements with a trancluding directive. This directive changes content of the row (template) and ng-repeat does not work correctly (when removing/moving rows), because ng-repeat works with the original template (elements).

This changes ng-repeat behavior to traverse the DOM to find current elements everytime we are moving/removing rows (if the template has multiple elements).

Closes #3104