adding code to do NAT type detection, plus other changes, see comment below. 

1. updated package dependency to use newer freedom and uproxy-lib
2. Adding server code for NAT detection, and server testing client, both in python. 
3. Update javascript (typescript) code to do NAT type detection. 
4. remove end-2-end testing code. Revised version is now available in uproxy-end-to-end as freedom module. 
The names here are pretty opaque, can you thin kof more descriptive names? Also, some of them aren't used anywhere, e.g. `extern_ip0`.

Same for `jsonclient.cfg`.