Square, PayPal, Intuit, Verifone -- the mobile payments field (and we're not talking wallets here) is seriously crowded already. So, the question is then, why on Earth would Groupon want to join the fray? We're not entirely sure, but VentureBeat is reporting the coupon service is preparing to do just that. According to a source within the company, Groupon is testing card-reading dongle and payment platfo
