Download subs

Opens the subs addon or download first matching sub (it set in xbmc)
Merge pull request #151 from Hellowlol/sub

Download subs button
Fix dash nzbget

Should close https://github.com/styxit/HTPC-Manager/issues/155
Merge pull request #157 from Hellowlol/dash-nzbget

Fix dash nzbget so failed downloads gets marked with x