1. sync important fields of store.pods[id]; 2. sync between yjs and database

[lihebi]

In collaborative editing, only yjs.nodesMap is synced, but the store.pods[id].xxx fields are not updated. We need to sync the store.pods, otherwise, later operations might create issues, e.g., #136 (comment).

We also need to design carefully to maintain consistency between yjs and the database.

Ref: #136

Fields:

• position (after dragging)
• parent/children (after dragging into a scope)
• content