Public server mode

To test it, launch the daemon with the following option: -public_server_mode=1

Requires its Core counterpart (miguelfreitas/twister-core#183).

Don't allow all IPs to access your server yet. API calls are restricted in this mode, but I don't know much about network security. If you plan running a public server, wait for the experienced developers to verify if it is really safe to run openly.