Issue #2566771 by Cottser, mortendk, jstoller, LewisNyman, mdrummond, Gints Ērglis, sqndr, Chernous_dn, Manjit.Singh, axe312, emma.maria, davidhernandez, lauriii, jaxxed, akalata: [Voltron patch] Move all remaining *.theme.css to Classy

Issue #2378095 by Wim Leers, Devin Carlson: Convert all remaining attached individual CSS/JS assets to attached asset libraries