Etsy, the Brooklyn-based marketplace for handmade knicknacks, said Monday it has acquired music-gear site Reverb for $275 million. Reverb — backed by Groupon co-founders Eric Lefkofsky and Brad Keywell, as well as PayPal co-founder Max Levchin and venture capitalist Roger McNamee — is a marketplace for new and vintage musical instruments and accessories, from Fender...