change the wifi and mqtt setup to WiFiManager

[roeidalm]

First, amazing project!
second,
if you integrate the WiFiManager to your code. that will can be use in the further when someone change his SSID or something

https://github.com/tzapu/WiFiManager

[se1exin]

@roeidalm wow I didn't know the WiFiManager library existed, it looks super useful! I'm working on a new ESP8266 project at the moment so will test it out on that, afterwards I will integrate into this project