Fixed: New AboutPanel.xib replaces older CIB file

With the death of Atlas CIB files can no longer be edited directly. This commit replaces a CIB-only version of "AppKit/Resources/AboutPanel.cib" with a XIB-derived one that can be edited in Xcode.

This commit also moves some of the formatting of the about panel into the IB file (c.f. the FIXME note).