Content directory integration work, part 2: Update proposals-codex pallet

[iorveth]

1. Remove content-working-group module.
2. Refactor content-working-group module related functionality, using new working-group. (make all content-working-group proposals work for the new working group module)
3. Update node proposal_encoder.rs
4. Replace versioned-store & versioned-store-permissions dev dependencies with content-directory module, update mock implementation.

[iorveth]

Closed by #1366