Hi!

Because a “connection error” message is displayed to the first player that tries to join when the server is stopped, I wanted to be able to customize it (useful for translating it to native language or providing more specific instructions, i.e. “try again in a minute”). So I made a few changes that allows everyone to set their own message via msh-config.json. This is my first time writing anything in Go, but I deployed these changes on my own server and it has been working great.

I thought maybe other users would appreciate this feature, so if you want, feel free to merge it. Thank you for this great project!