* [instagram] Gracefully handle possible 'HttpErrorPage' in _extract_page()
`HttpErrorPage' is returned in shared_data at least when not authenticated or
when trying to fetch other users saved medias
(i.e. `instagram.com/<user>/saved/').
Gracefully handle it by returning nothing.
* [instagram] Add support for user's saved medias
(Please note that this need the user to be authenticated and they can
only see their saved media (not other users ones).)
Close#643.
* [instagram] Bump copyright year