Expose the shared NSOperationQueue and add custom queue support.
Change how MBRequest handles operation queues.

You can now set the operation queue of any request individually. You
can also now access the MBRequest shared operation queue from a public
MBBaseRequest class method.

These changes necessitated removing a couple of public methods,
including MBBaseRequest's -scheduleOperationOnQueue: and
-sharedRequestQueue methods. Instead, override +sharedOperationQueue
and/or use the operationQueue property on MBBaseRequest.
Remove deprecated method.
Add cookie logging.
URL encode query paramemter keys.