Implemented very decent outputs property.

Usage Example:

    >>> ops = client.outputs
    >>> for op in ops:
    ...     print(op.oid, op.enabled, op.name, sep='\t')
    ...     # Enable all of them
    ...     op.enabled = True
    ...
    0 True  AlsaOutput
    1 False HTTPOutput

Test don't pass yet. Probably a memory leak.