Epic: Refactor

To enable caching:

• Move all non-UI workspace state and actions to Redux
• Normalize actions - don't refer to global pointer ids, only refer to workspace-relative pointer ids
• Record all normalized actions a user takes on the server

To enable simple versions/diffs, staleness computation (including due to budget change), pointer unlocking, pointers to blocks (scratchpad, child's answer, etc), and reflection (pointers to children that include pointers to their children, etc):

• Change representations to unify workspaces, nodes, and pointers