Database performance improvements
Database performance improvements

Folders with large numbers (>100) of unread articles were
loading after a delay. Profiling showed a lot of time spent
in FMDB's `stringForColumnIndex` method so I replaced a bunch
of them with `intForColumnIndex` where it made sense.

josh64x2/vienna-rss,tothgy/vienna-rss,dak180/vienna,Eitot/vienna-rss,Eitot/vienna-rss,josh64x2/vienna-rss,ViennaRSS/vienna-rss,ViennaRSS/vienna-rss,dak180/vienna,lapcat/vienna-rss,lapcat/vienna-rss,tothgy/vienna-rss,dak180/vienna,Eitot/vienna-rss,ViennaRSS/vienna-rss,barijaona/vienna-rss,josh64x2/vienna-rss,lapcat/vienna-rss,barijaona/vienna-rss,josh64x2/vienna-rss,Eitot/vienna-rss,tothgy/vienna-rss,barijaona/vienna-rss,tothgy/vienna-rss,ViennaRSS/vienna-rss,barijaona/vienna-rss,lapcat/vienna-rss,dak180/vienna,ViennaRSS/vienna-rss,josh64x2/vienna-rss,barijaona/vienna-rss