Multiple improvements and fixes from dev environment

[proditis]

This PR includes the following

• Improved backend/frontend/player/index gridview
• add a new sysconfig hide_timezone, causes the timezone information to be hidden from the frontend
• add a new sysconfig guest_visible_leaderboards to enable/disable access to the leaderboards by guest users (fixes add configurable flag for publicly visible leaderboards #1119)
• Improved backend/yii vpn commands documentation, error handling and operations
  • fixes Implement frontend/player/kill-vpn action on mUI #1130
  • fixes Streamline backend vpn/load and vpn/save commands #1129
• Updated vpn docker entrypoint script to perform a backend/yii vpn/load on the existing configuration file
• Introduce verifymail.io fixes Create verifymail.io singup and email change validation module #1116