Implement Next and minimal backend

[serejandmyself]

Overview

• The current demo version does not have a backend, only UI
• Data has to be structured, indexed, stored when appropriate
• The back-end should be added gradually, with historical data less prioritized (see API doc)
• Citizen Web3 provides public endpoints, which should be collected from @alibabaedge

API

• API doc (shared via team chat): #56 | #52 |

Metrics

• Val: #42
• Networks: #145