Elton and Bill: BFFNoah Gundersen, Sea Fever at the Crocodile, 8 p.m., $8Young folk songwriter Noah Gundersen’s headlining the Croc tonight; guess we’re not the only ones who liked his album.Elton John and Billy Joel at Key Arena, 7:30 p.m., $54-$180, all agesElton John and Billy Joel: like peanut butter and chocolate.