#1866: support e-hentai source redirection

* hopefully prevents error pages when the url during upload expires
* makes use of file sha-1 hash and filename in the url to query the e-hentai search page
* the file hash by itself is enough to generate a result but the filename is also added for completeness (the page displays the filename being searched)
* ip addresses, port numbers, and unix timestamps validation can also be added later
* a better solution maybe is to get the gallery ids and gallery tokens directly