Few fixes for 'lostfilm' plugin

[repa4ok]

• bt_backend:more convenient canonical_url: from my point of view it is more convenient to use 'canonical_url' provided by plugin, not those one constructed dynamically. also, new constructed url passed to backend_play_video, so probably it is possible to update playing count for both urls.
• es_string: fix for "utf-8" encoding: I'm experiencing error with handling one URL because it returns charset as "utf-8" (with quotes). it would be nice if you know a better way to fix that :)