Revert "MIKMIDIObject's name property is now publicly readwrite."

This reverts commit 13f17099aa8f55ca18e4b50aea40a1f7d25633fd.
Added -[MIKMIDIEndpoint isPrivate]
Fixed bug in -[MIKMIDIDeviceManager removeInternalVirtualDestinationsObject:]
Issue #6: MIKMIDIDeviceManager's virtualSources and virtualDestinations properties emit KVO notifications, and NSNotifications are posted when virtual endpoints' private status changes.
Added some minor code useful for debugging to MIDI Testbed app delegate.
Issue #6: MIKMIDIDeviceManager's virtual sources are updated in response to endpoints being added and removed.