Graceful handling of long text in article list’s cells

Solves issue #307
Earlier check that an article has to be marked read
Fix article list not being updated on group folder

As seen in <http://forums.cocoaforge.com/viewtopic.php?t=26595>
Serialize updates of folder’s count of unread articles

Follow up on http://forums.cocoaforge.com/viewtopic.php?t=26592
Force article view to not cache

Attempt to solve issue at http://forums.cocoaforge.com/viewtopic.php?f=18&t=26591
Small optimization
Merge pull request #308 from barijaona/topic/vertically-center

Graceful handling of long text in article list’s cells
Merge pull request #309 from barijaona/topic/mark-read

Fixes/improvements to marking read a folder
Upgrade version number to 3.0.0 RC 5