The proxy API is the one that we would like to expose for applications
and the other API is used internally when implementing modules or
factories.
The current pw_core object is really a context for all objects so
name it that way. It also makes it possible to rename pw_core_proxy
to pw_proxy later.
Remove the parent_id from the global event. Remove the parent
and owner from the global object.
Use properties instead to mark parents and owners of objects.
Properties are easier to control for client exported objects and
usually a simple parent/child is not enough. For example, a client
exported node has the client as a parent but also the factory that
created the node.
Make a set-prop command to set a property from the config file
into a pw_properties. Pass this to the pw_core_new() and the
main-loop to tweak some stuff.
Move some warns to errors
