factor out wifi code

[phatpaul]

The WiFi code in this httpd repo is outside the scope of an http server. It requires maintenance as the ESP-IDF SDK changes and it is application dependent.

Anyone object if I factor out the wifi code and move it to the example repo: https://github.com/chmorgan/esphttpd-freertos ?
Or should the wifi code be moved to another git submodule (like we did with espfs)?
Or it could be replaced with a newer solution like https://github.com/farpatch/esp32-wifi-manager ?

BTW cgiflash and vfs could also be factored out... Thoughts?