Upgrade to lb4

[f-w]

Since there is no automated upgrade path, a re-write is necessary. Therefore this would be a major undertake.
High-level migration work involves

• getting familiar with Loopback v4 and Typescript
• gap analysis - find alternative implementations of features available in v3 but missing in v4 which include but not limited to
  • Environment-specific config
  • Operational hooks
  • Mix-ins
  • User Management (auth & autho)
• setup test framework
• rewriting app and test scripts
• work out data migration strategy, if necessary