Handle Esc key ⎋ when editing a feed name

Fix issue #276
Upgrade InfoWindow.nib to modern Xcode interface builder

This makes things much easier for translators.
Fix an infinite loop with duplicate folder names
Handle images defined by embedded data

Fix issue #265
Vertically center images and progress indicator on Folders list

Fix issue #277
Simpler progress indicator centering on article list
Merge pull request #289 from barijaona/bugfixes

Important bugfixes
Upgrade version number to 3.0.0 RC 2