Bring back the channel object. Making a node and port on the client side
was rather awkward because of the async nature of many methods. It feels
better to have a specific communication channel object to interface with
a server side port.
Use port activate/deactivate to start/stop streams
Remove links from the ports. We let other objects install a callback on
the port to receive and route buffers.
Remove the client object, it is not very useful now that we have the
nodes.
Fix some properties on the proxy objects.
Use sendmsg and recvmsg directly because the GIO ones do allocations.
make pinos_properties_merge and use it to combine properties from nodes
and ports.
A port is an input or output on a Node.
Channels are created from the ports and inherit the direction of the
port.
do automatic port selection based on the direction and caps and
node/port name.
Simplify stream_connect by passing the direction.
Fix pinossink to connect in setcaps so that we know the format and can
select a good sink to connect to.
Rename the source-output object to channel because it is used for both
input and output.
Start the beginnings of sink support. This will make it possible to make
pinos consume data as well as provide data.
