Enable automatic timed and scheduled messaging

It would be great if admins could set automatic notifications to be displayed to all players, i.e.:

• Admin enters /admin timed 15, "Thanks for playing on My Awesome Server! Type /motd for server info", white in chat
• Every 15 minutes users will see a white notification that lasts for 10 seconds that says "Thanks for playing on My Awesome Server! Type /motd for server info"

and

• Admin enters /admin scheduled 03:59, "The server will restart in one minute, stop your ships!", red in chat
• At 3:59 AM server time users will see a red notification that lasts for 10 seconds that says "The server will restart in one minute, stop your ships!"

Obviously the color argument could be optional, default to white. And you could add another optional arg for notification length.

Now that you guys have implemented server-client messaging this should be much easier to achieve.

Start by locating the admin command handling and the server-client messaging implementation mentioned in the issue. Determine how timed and scheduled commands, notification color, and display duration should fit the existing command conventions. Done means admins can configure both recurring and daily notifications, with the stated defaults, and players receive them as described.