Improve responsiveness of Vienna UI during heavy database activity

Fixes Issue #202. Also Vienna forums: http://forums.cocoaforge.com/viewtopic.php?f=18&t=26232&p=137304#p137292

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The replacement of SQLiteLib with FMDatabase is now complete on Echelon9's Github branch.
The FMDatabase middleware looks to do a better job, on default settings, of handling requests to and from the on-disk SQLite database that Vienna uses behind the scenes. 

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Given a few days' experience with the new FMDatabase-rearchitecture Github branch, I am increasingly confident it is faster at refreshing articles and generally more "snappy" due to the lesser prevalence of UI blocking.

Qualitatively, I'm no longer seeing the occasional hang of one or two RSS feed requests amongst my feeds that I used to see before.

Testing an extreme case of 330+ feeds, current Vienna was near completely unusable, but with FMDatabase browsing through downloaded articles was fairly snappy while the remainder refreshed.