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.
Use some python [magic](http://learnpythonthehardway.org/book/ex28.html):

1.  `''` evaluates to `False` inside a boolean context

1. The `or` operator is lazy: if the first argument evaluates to `False`, it will return the second as it is.

Thus:
```python
shipping_price = _order['shipping_price'] or 0
```