Add accessory information fields to config UI

[NotBobTheBuilder]

I wanted to move my mqttthing devices across hosts without changing the serial numbers. I found that could be achieved by altering the config, and that thought it would be an improvement if you could change those fields directly in the UI.

The fields I added to the UI are:

• manufacturer
• model
• serialNumber
• firmwareVersion

I identified those from here:

https://github.com/arachnetech/homebridge-mqttthing/blob/cb399ac261063650a892757b526c2238310f65fe/index.js#L25-L32

Hope this helps!