MidiDevice: Add support for making direct connections between ports

The output port of one device can be connected to the input port of another
device using the new MidiDevice.connectPorts() method.
This allows an application to direct the output of one device directly
to the input port of another without having to copy data from one to another.

Change-Id: I4d361c4e0950b9b9516b0c2f0c158677b1aca208