Issue #2301239 by pwolanin, dawehner, Wim Leers, effulgentsia, joelpittet, larowlan, xjm, YesCT, kgoel, victoru, berdir, likin, and plach: MenuLinkNG part1 (no UI or conversions): plugins (static + MenuLinkContent) + MenuLinkManager + MenuTreeStorage.
Issue #2289063 by larowlan, andypost | Berdir: Change contact message entity to behave more like a normal entity.