emqttd#781: Update README for EMQ 2.0

emq_dashboard#84: Show the Cluster Status of Node

emq_dashboard#79: disc_copies to store mqtt_admin table

emq_auth_clientid: disc_copies to store mqtt_auth_clientid table

emq_auth_username: disc_copies to store mqtt_auth_username table

emq_mod_subscription#3: Remove emq_mod_subscription table and module.subscription.backend config

emq_plugin_template#5: Unregister Auth/ACL modules when the plugin unloaded