Added two new options + Bugfix in description

Added two new options
---------------------
preferred_hoster_only: Only hoster in the hoster list will be accepted.
handle_no_url_as_failure: When no suitable URL is found the plugin lets the task fail and therefore the RSS-Post will be scanned again the next time.
-> Ticket #1862

Bugfix description
------------------
Ticket #1826;Ticket #1324