* populate most session item properties from create-item.lua to keep
things more compact and readable
* use a standard naming scheme for the session item properties
* use session item properties instead of node properties in policy-node.lua
* improve policy-node's performance by converting the properties dictionary
less times for each session item
* refactor some policy logic and make things slighly more readable
* change the accepted values for 'context' in wp_si_linkable_get_ports();
use "input" and "output" to keep things clear, because the previous use
of NULL and "reverse" were implying that a node has only one "standard"
direction, but this is complicated for sinks w/ monitors and duplex nodes
* allow using monitors (which are Audio/Sink nodes in fact) as sources
* treat Audio/Duplex nodes as sinks, like p-m-s does
* respect the "stream.capture.sink" property of streams
Fixes#66
If 'disable.dsp' is set to TRUE, the adapter will always be configured in
passthrough mode. Then, if 2 adapters want to be linked with different formats,
the si-standard-link session item will automatically reconfigure one of the
adapters in convert mode so that the format matches.
And be careful not to handle nodes created by si-audio-endpoint,
by using a specific property for that.
Also, use Audio/{Source,Sink}/Virtual as the media class of null sinks
created by si-audio-endpoint, it sounds more appropriate.
Fixes#34
