[WIP]Issue #485 Relay namecoin id to other nodes

1) As requested in #957, we changed namecoin_id column to lowercase. 

But! Someone who had already upgraded their database with the old migration scripts will still have their column named with a capital, and there's no easy way to get rid of it since sqlite does not support DROP COLUMN (issue #955). New databases created will work fine of course, and rerunning the migration4.py script will probably do it as well. Let us know if you want us to cancel this modification.

2) We begun working on issue #485 by @dionyziz . We added the namecoin of the sender to the rest of the information in the 'start_handshake' and 'send' methods in CryptoPeerConnection and we also stored the namecoin the user entered with the rest of his info in CryptoTrasportLayer. Is this the right way to do it? Should we change anything else? We need a little feedback here @gubatron , @hoffmabc :) 

3) As it is now, TransportLayer does not have a 'namecoin' field. Should we add a namecoin field in there, and treat it in the same manner as nickname?

4)Should we add the namecoin to the 'ok_msg' in transport.py (line 136)?

5)We see that you sign the information *before* you encrypt it. Is that intended? afaik this is not secure...
If `guid` can never be `None`, you can avoid double-checking by using
```python
return data.get('openbazaar') == guid
```