Refactored outline provider to work with INode instead of IElement

The original implementation failed when there were comments on the
documents root level. By using INode instead the system should be more
future proof.

Change-Id: I4536946aa024317f2e917c4b9307caea3553f1dc
Signed-off-by: Carsten Hiesserich <carsten.hie@gmail.com>
6 files changed