Returns potential Link or Stream sources.

def link_sources(self):
        "Returns potential Link or Stream sources."
        if isinstance(self, GenericOverlayPlot):
            zorders = []
        elif self.batched:
            zorders = list(range(self.zorder, self.zorder+len(self.hmap.last)))
        else:
            zorders = [self.zorder]

        if isinstance(self, GenericOverlayPlot) and not self.batched:
            sources = []
        elif not self.static or isinstance(self.hmap, DynamicMap):
            sources = [o for i, inputs in self.stream_sources.items()
                       for o in inputs if i in zorders]
        else:
            sources = [self.hmap.last]
        return sources