Add, change or delete blocks

Change some blocks of a slide and leave the others alone, in one step: "add": new blocks [{"type", "props"}] (placed on top, or at the bottom with "at_bottom": true); "update": [{"id", "props"}] -- only the given props change. The same props for several blocks at once, like selecting them in the editor: {"ids": [...], "props"}; or for a card and everything drawn on it: {"inside": <id of the card's background block>, "props"} -- that block and every block lying within its rectangle (props a block type does not have, like "link" of a code block, are skipped for it); "delete": [block ids]. Returns the slide (ids only unless "response" is "full").