fix: null message crash and drop array messages

[Flechaa]

Previously in PR #48, all JSON releated crashes were supposed to be fixed, however I completely missed out that typeof doesn't catch things like null in JSON since they are considered an object in JavaScript.

Also arrays are not used for messages in Rotom so those were also checked and dropped in this PR.

Snippet that replicates the crash:

const WebSocket = require("ws");

const ws = new WebSocket("ws://localhost:7070/control", {
    headers: {
        "x-rotom-secret": ""
    }
});

ws.on("open", () => {
    ws.send("null");
});