Hide feeds

Hide a feed when the title starts with an exclamation mark. Useful for sites with a lot of similar feeds, like heise (news, security, developer, ...).
```
"query:heise:tags # \"heise\""

# these feeds doesn't get displayed
http://www.heise.de/newsticker/heise-atom.xml "!online" heise news
http://www.heise.de/open/news/news-atom.xml "!open" heise news
http://www.heise.de/security/news/news-atom.xml "!security" heise news
http://www.heise.de/developer/rss/news-atom.xml "!developer" heise news
http://www.heise.de/netze/rss/netze-atom.xml "!netze" heise news
```
So you have just one query feed and not 5 feeds (plus a query feed).