Plugged UPnP Port Mapping.

Hi there, first serious commit.
Please checkout this branch, start OpenBazaar and let me know if the port mapping is working for you.

If I didn't make any mistake, it should be mapping the internal port 8888 to external port 12345.

The router of my current network is a little funky so I can't test properly. 

Note: Looking at all the other port mappings on my router, I notice that they usually map the same port number, if you have issues between 8888 -> 12345, hardcode port 12345 on tornadoloop.py before the OpenBazaar server starts listening. If it works this way, and not the other way around maybe I made a mistake somewhere and confused internal port with external, at the moment I have no way of testing, so I need your help.

cheers.