[functions] resorted to dropbox for `adhoc` hosting

Useful links if decide to try local server again:
* https://blog.httpwatch.com/2013/12/12/five-tips-for-using-self-signed-ssl-certificates-with-ios/
* https://github.com/deckarep/EasyCert/
* https://coderwall.com/p/cbyxyq?&p=2&q=
* https://www.srvdir.net/
* https://gist.github.com/willurd/5720255