Add DNS server

Android and Windows devices don't support mDNS. Write a UDP DNS server component to capture all DNS queries and reply as necessary.

Posts to respond to once done:

• https://esp32.com/viewtopic.php?t=8123
• https://www.esp8266.com/viewtopic.php?t=12369

To look at:

• https://esp32.com/viewtopic.php?t=3761
• https://github.com/espressif/esp-idf/blob/master/examples/protocols/sockets/udp_server/main/udp_server.c
• https://github.com/espressif/arduino-esp32/blob/master/libraries/DNSServer/src/DNSServer.cpp