v4.0.0

• Support GraphQL v15
• Support GraphQL Config v3
• Update every dependency to latest
• Move shared parts of logic under @graphql-cli scoped packages
• Use Yargs instead of Commander.js
• Add validate, coverage, diff and similar commands - GraphQL Inspector
• Use GraphQL Codegen in codegen command
• Replace playground with serve command
• Replace get-schema with introspect command
• New Plugin System
• Use Graphback
• Bug fixes