Issue #2491155 by mikeburrelljr, Mac_Weber, opdavies: Update drupal.org and kernel.org URLs in core modules (Follow-up to 2489912)

Issue #2389735 by lauriii, iMiksu, davidhernandez, larowlan, loopduplicate, LewisNyman, Wim Leers, dawehner, Cottser: Core and base theme CSS files in libraries override theme CSS files with the same name

git commit -m 'Issue #2377397 by Wim Leers, alexpott: Themes should use libraries, not individual stylesheets'

Issue #922696 by mgifford, EvanDonovan, LewisNyman, stpaultim, jensimmons: New methods, standards for describing core themes on themes admin page (was Theme screenshots do not have adequate alt text...).