[FileCache] Ignore 'format' when generating the file name
[FileCache] Ignore 'format' when generating the file name

Previously for each requested format a new cache file was created,
though the data is the same. With this the file name no longer depends
on the requested output format.

GregThib/rss-bridge,simonbru/rss-bridge,sebsauvage/rss-bridge,RSS-Bridge/rss-bridge,mro/rss-bridge,Frenzie/rss-bridge,LogMANOriginal/rss-bridge,teromene/rss-bridge,kranack/rss-bridge,RSS-Bridge/rss-bridge,kranack/rss-bridge,ORelio/rss-bridge,simonbru/rss-bridge,Riduidel/rss-bridge,polo2ro/rss-bridge,ORelio/rss-bridge,griffaurel/rss-bridge,ORelio/rss-bridge,RSS-Bridge/rss-bridge,LogMANOriginal/rss-bridge,mro/rss-bridge,kranack/rss-bridge,teromene/rss-bridge,Frenzie/rss-bridge,Riduidel/rss-bridge,Riduidel/rss-bridge,kranack/rss-bridge