Refactor section traversal
Remove element accessor

The element variable is only accessed from within the class, so we do
not need a public accessor
Rename section to root

The word "section" is used in a lot of places so we rename the
anchorpoint of a type inside a specific configuration file to root.
Add feature to remove a key

If a property defines a valid value of :absent we'll now remove the
corresponding nimsoft key if the property is set to absent.
Add new type nimsoft_queue