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Closes #4611

Refactored generateXmlFromNodes to pull the urlElements itself from
sorted values in the lookup

Added some checks to existing unit tests to validate ordering.
Return computed url with post object

closes #4445

- post model gets permalink format
- post model queries urlPathForPost to return computed url
- url helper modified to use post url
- urlForPost method abolished and replaced where necessary
- updated tests
Add Tag Meta View

Closes #4509, Closes #4615

- Adds meta title & meta description input fields
- Autosaves meta data
- Shows SEO preview (falling back to tag name & description if meta not supplied)
- Adds `type="button"` to delete button (which closes 4651)
Merge pull request #4565 from PaulAdamDavis/tag-meta

Tag Meta Screen
Merge pull request #4616 from jgable/siteMapOrder

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Merge pull request #4529 from cobbspur/permalink

Return computed url with post object