Update "Photo - Flickr" Extractor

* Fix a RegExp for user icon
* Make RegExps strict
* Add support for video thumbnail
* Add support for lightbox page
* Change an empty title to "Untitled"
* Improve getImageID() for context check
* Rename ID_RE to IMAGE_RE
* Rename IMAGE_PAGE_RE to PHOTO_PAGE_RE
* Add getImageURL()

This CL is follow-up for 0b55afd318159cf13924ece59b3867fe915aebf0.