Don't mark xmlwalker folder URLs as seen
Publish non-xmlwalker items from other sources by default
Use normalized ids for xmlwalker content items
Add relatedItems to default redirector keys
Don't add redirections for the same path
xmlwalker pipeline fixes:

* Use xmlwalker aribitrary fields instead of separate sections
* Add relatedItems, disabled by default
* Defer keys that need redirections added before they can be processed
* use options instead of variable substitution where possible
* use different key names for dummy inserter sections