Inserting a rap number into a 1930s Brechtian play-with-music takes a certain sort of chutzpah. Managing to elevate the work in the process: now, that’s just impressive. Catalyst Theater Company has definitely improved on the text of its latest production, Roundheads & Peakheads, a didactic little parable about class warfare and political maneuvering. The work’s connection to the current economic climate is undeniable, but Catalyst doesn’t dwell too much on beating us over the…