Issue #2349461 by Jelle_S, mdrummond, attiks, Wim Leers: Move fallback image style into the responsive image style entity

Issue #2383165 by sidharrell, alexpott: ResponsiveImageStyle config entities should depend on the image styles they use

Issue #2260061 by Jelle_S, attiks, Wim Leers, mdrummond, mgifford, holist: Responsive image module does not support sizes/picture polyfill 2.2