Protect flash from wear out by Wifi.begin()

[benjaminSchilling33]

Hi @alfkoehn,

I just saw your CCCS talk from rc3 and noticed that you are using an ESP8266.

A common problem that may occur when using Wifi.begin is that it can wear out the flash if called every once in a while (e.g. when the device is reset regularly).

Therefore it is useful to disable the persistent storage of the Wifi credentials.

For more details see: https://github.com/esp8266/Arduino/issues/1054