remove positional exchange type, and use the exchange_opts dict instead,...

... allowing the override of exchange_type from SimpleQueue constructor.

Before this change, the following script fails:

```
from kombu import Connection
from kombu.pools import connections
connection = Connection('amqp://guest:guest@localhost:5672')
with connections[connection].acquire() as conn:
    with conn.SimpleQueue('callhome_logging', exchange_opts={'type': 'fanout'}) as queue:
        while True:
            message = queue.get(block=True)
            message.ack()
            print message.payload
```

With this exception:

```
$ python test.py
Traceback (most recent call last):
  File "test.py", line 5, in <module>
    with conn.SimpleQueue('callhome_logging', exchange_opts={'type': 'fanout'}) as queue:
  File "/Library/Python/2.7/site-packages/kombu-3.0.0a1-py2.7.egg/kombu/connection.py", line 709, in SimpleQueue
    exchange_opts, **kwargs)
  File "/Library/Python/2.7/site-packages/kombu-3.0.0a1-py2.7.egg/kombu/simple.py", line 115, in __init__
    exchange = entity.Exchange(name, 'direct', **exchange_opts)
TypeError: __init__() got multiple values for keyword argument 'type'
```