Refactor configuration

[kiootic]

• remove msgpack
• use https://github.com/kubernetes-sigs/yaml for yaml
• use https://github.com/iawaknahc/jsonschema for validation
• app_id optional (default constant in single teanant)
• hostnames in config (merge from VALID_HOSTS)
• watch config (directory)
• delete version
• move db config
  • db, redis -> credentials config
• delete master key & access key
• delete removed feature config
• local development mode flag (use viper & cobra?)
• delete default smtp etc config
• enable file loader by default

•  type PrivateConfig struct {
    Secrets []SecretDef
    Credentials []CredentialDef
    }
   type AppConfig struct {
    ID string
    Hosts []string
    // ...
   }