Fix comments and unittest for market.py and style

Trying to make the right commit to  the develop branch.
@Renelvon I think the indentation you linked to isn't PEP8-compliant.  I think it should be like this:
```Python
t = Thread(target=self.transport.dht.iterativeStore,
           args=(self.transport, contract_key, str(signed_data), 
                 self.transport.guid))
```
I'll add this change to my PR https://github.com/Ignat99/OpenBazaar/pull/1