Fixes for 3696, 3475

Commit e0b27c5eeb428e895ed395e4247edb075 allows to hide listened and unneeded podcast episodes.
I have found a broken feed, so  6e5bf75d240192ef0974183364378d5a31dcb332 is needed to "fix" it 
http://feeds.feedburner.com/reasonabledoubts/Msxh?format=xml

I think that ParseRFC822DateTime needs some more work.
Instead of having two QSettings objects, the convention is to have one and call endGroup on it:

QSettings s;
s.beginGroup(LibraryView::kSettingsGroup);
use_pretty_covers_ = s.value("pretty_covers", true).toBool();
s.endGroup();
s.beginGroup(kSettingsGroup);
...