We need different export decorators for the different libs.
For now no actual change though, just rename before the release,
and add prelude headers to define the new decorator to GST_EXPORT.
Add methods to add/remove the providers that should be hidden by this
provider. Also make a method to get a list of hidden providers.
This makes it possible to have multiple systems monitor the same devices
and remove duplicates.
Add a property to see all devices, even duplicate ones from hidden
providers.
