[fix] solidtorrents engine: JSON API no longer exists

The API endpoint, we where using does not exist anymore.  This patch is a
rewrite that parses the HTML page.

Related: https://github.com/paulgoio/searxng/issues/17
Closes: https://github.com/searxng/searxng/issues/858



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>