Django-pagetree

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* new "generic" views for view, edit, and instructor view pages
* default page.html, edit_page.html, instructor_page.html, and
menu.html templates included.
* removed admin views (sdreher)

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* enforce slug validity

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* proper fix for request context bug

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* request context patch

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* truncate slugs to 50 chars, since that's what they are limited to in
the db

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* enforce uniqueness on UserPageVisit and UserLocation