PEP8 openbazaar.py through ws.py

PEP8 clean up 3 of 3.  Orders.py has some very deeply nested dictionaries which necessitate long lines.  This situation may suggest minor future refactoring of the affected methods.
No need for backslashes of either kind:
```python
offer_data_json = '{"Seller": {%s' % (
    offer_data[:index_of_seller_signature]
)
```