You can build an entire world on one song. Meet Hallstrom. Tom and Kate, just two of a much larger “family” band. Key track on their latest CD, “Out on the Borderlands, Down in the Valley”: “Borderlands.” Hallstrom opened for Griffin House last night at the Tractor Tavern, in Ballard. These folks need to be on vinyl, to highlight their lo-fi aesthetic and their rescued pianos and smokey guitars. Songs from the #435 bus, full of heart and thunder and the search for home. More please.