Transmogrify.siteanalyser

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- show error if text is None
- fix bug with bad chars in rewritten links
- fix bug in losing items
- add hidefromnav blueprint. does manual hiding

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- remove nulls from links which cause lxml errors
- summarise info in log to single entry

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- condition was in the wrong place. resulted in dropping items
- improve logging
- handle default pages that don't exist

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- fix bug where _defaultpage wasn't being relinked

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- fix bug in quoting links in relinker

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- Add conditions to site analyser blueprints