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.
Detect a format change in the payloader and post an element message.
Catch the format change element message in the client-source and use it
to update the format and possible formats in the source and source-outputs.
Make sure we unref the source-input when it is removed.
When the source-input is removed, we should also unref the source. Do
this by adding the source as data for the source-input and unreffing it
when the source-input is freed.
