Current Glade versions want object IDs to be unique, but currently
pavucontrol.glade shares some IDs between the top-level windows. I guess
this used to be OK in the past, and the "interface-naming-policy
toplevel-contextual" comment in the beginning of the .glade file
probably has something to do with this. I want to update the .glade file
to be easy to work with current Glade versions, so I will remove the
duplicated object IDs.

The first IDs to change are the "channelsVBox", "nameLabel",
"boldNameLabel" and "iconImage" IDs. These were used by
MinimalStreamWidget to create widgets for both devices and streams, but
now that the IDs are different for devices and streams, the widgets have
to be created by the subclasses.

MinimalStreamWidget doesn't need the Gtk::Builder in its constructor any
more, so remove that parameter to avoid warnings about an unused
variable.