Fixed router port forwarding so will try UPnP if NATPMP fails.  Updated angularjs-file-upload version to 1.0.0 since 0.1.4 tag was no longer available
NAT fixes.

* Move all nat related code over into the nat package.
* Merge updates from mux.
* Return loopback if external address cannot be determined.
* Do not publish into rendezvous if extHost is loopback.
* Use fmt.Sprintf() instead of string concats, much easier to read.
* Change command line flags from useXXX to onlyXXX to better reflect usage.
* With Airport, the timeout must be non-zero.
  We might need to maintain a set of defaults for each router :(