Use search backend for page autocomplete.

Please verify your current install works after applying this.

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We now use haystack (and thus solr) to do pagename autocomplete.  This will provide increased performance and better result matching.  Before, we would only match on name__istartswith on pagename, but now we'll match substrings.  I am sure there is room for improvement here, but this should be better than it was.

Added migrations for the page app (convert_to_south) as well as a data migration that runs the update_index management command.

Fixes #76.