LEAN-1138 Taking out react components out of Prosemirror DOM tree.

Closes LEAN-1138. Captions didn't work correctly because passing prosemirror dom views into react and rerendering them inside caused prosemirror to loose control over position and cursor. T avoid that we won't implement any more react views for the entire nodes but rather will insert react elements as separate auxiliary elements (dropdowns, menus, etc.).