Fixes #22
Fixes #6

Java side:

• WebsocketJsonMessage class for the message format.
• MinecraftServerIdentifier class to properly identify the "server" name and a unique identifier.

Front-end:

• New message_types.mjs module containing the front-end implementation of the new structured messages.
• Reworked chat.mjs to handle the new structured message format.
  • This includes handling the new timestamps. This includes using them for error messages.
• Added: utility function to create timestamps.
• Sneaky refactor of the CSS to be more consistently use rem.
• Removed functionality for stored messages from the front-end code. It didn't make sense to me to try and migrate these somehow and the next PR from me will very likely be tackling Store chat messages per server within the minecraft config directory instead of using front-end. #3

Example message

{
    "timestamp": 1734794189937,
    "server": {
        "name": "Tildes MC Survival",
        "identifier": "4d311f91-6a27-31a3-b76d-3efe21dda823"
    },
    "type": "chatMessage",
    "minecraftVersion": "1.21.1",
    "payload": {
        "translate": "%s",
        "with": [
            {
                "text": "\u003c",
                "extra": [
                    {
                        "text": "creesch",
                        "color": "#0099CC"
                    },
                    {
                        "text": "\u003e ",
                        "extra": [
                            "Testing something with timestamp"
                        ]
                    }
                ]
            }
        ]
    }
}

Screenshot: