2sxc 08.04.00a with instant-insert, inner content and more

description will follow in a future version as soon as we're through with urgent quick-fixes that pop up in the first week

check out https://github.com/2sic/2sxc/issues?q=is%3Aissue+milestone%3A%222sxc+08.04.00+Inner+Content+Blocks+and+much+more%22+is%3Aclosed