This change refactors the code for inserting compatibility and
obsolete member pages into a qhp file, detaching it as a new
function and calling it when processing each node.

This ensures that members page, compatibility and obsolete
pages (html files) are added to .QCH files for all processed
nodes that have children or related nodes.

Also renames a variable ('node'->'nodeChildren') to prevent
shadowing.

Task-number: QTBUG-29314
Change-Id: Iccee70ba8768d48b24e68b08651043d0ce4a62a5
Reviewed-by: Martin Smith <martin.smith@digia.com>