Wifi multi network support for esp32/esp8266/PicoW

[tyeth]

This adds a new field called `alternative_networks' to the network_type_wifi object in the secrets.json settings file.

It's an array of objects (with fields network_ssid and network_password).

There is a maximum size of 3, although larger arrays will be tolerated only the first 3 entries will be used.

Example config:

{
  "io_username": "tyeth_demo",
  "io_key": "my_super_secret_adafruit_io_key",
  "network_type_wifi": {
    "network_ssid": "free4all",
    "network_password": "password",
    "alternative_networks": [
      {
        "network_ssid": "free4all_2G",
        "network_password": "password"
      },
      {
        "network_ssid": "HOTSPOT",
        "network_password": "password"
      },
      {
        "network_ssid": "Tenda_60C06C",
        "network_password": "password"
      },
      {
        "network_ssid": "THERMAL",
        "network_password": "password"
      }
    ]
  },
  "status_pixel_brightness": 0.2
}

[tyeth]

cleanup autoformatting and retest pico reconnecting between phone then home wifi

[brentru]

Overall this is a very solid feature implementation and I'll test it out on Monday. I've left comments requesting clarity and modifications.

Resolves #376

[brentru]

Consider changing this to else to avoid doing an extra call to strcmp and c_str

[tyeth]

The normal network ssid doesn't get added to the altNetworks, so this check needs to still happen.
It has just occurred to me that I failed to test one eventuality that the primary ssid could connect when none of the altNetworks were found (which would fail). I always had some alt networks in range.

I should move this to be a separate check, dropping the else, probably above the multi-network/altNetworks check as that will be the less common path.

[tyeth]

@brentru this should be good to go now. All feedback resolved except the "unused networks" error message, but left some not marked resolved so you see the explanations.
Let me know what you think