grl-launch: Add test_media_from_uri operation
grl-launch: Add media_from_uri operation

Given an URI and a source, it builds the GrlMedia that contains that URI in the source.
core: Append source ID in media_from_uri operation

If the source resolving the URI does not add the source-id, let's do it in the
core instead.

We always want the media coming with the source-id.