Include BSSID in scanned network results

Added a GET_IDX_BSSID_CMD SPI command to wifiHD. It's a fairly trivial change that allows users to fetch BSSIDs for scanned networks in the same way they fetch SSID, RSSI, and encryption type. Updated the Arduino WiFi library to reflect the change. 

I included the new wifiHD.hex and wifiHD.elf in the commit, but did not update the firmware version number.

I also fixed the numerous misspellings of "networks" in the Arduino WiFi library.