Fix the issue that invalid clients can publish will message. (emqttd#1230)

Fix Dashboard showing no stats data (emqttd#1263)

Support Persistence Logs for longer time (emqttd#1275)

Fix for users APIs (emqttd#1289)

emq-dashboard Plugin (emq-dashboard#154)

Improved the Dashboard Interface of Monitoring/Management/Tools.

Allow switching dashboard themes.