Sean Garballey, 23, a grad student at Suffolk, soundly defeated two opponents yesterday to gain a seat in the commonwealth's House of Representatives. Garballey will represent Arlington and part of Medford. Garballey is a recent graduate of UMass Lowell and has served on the Arlington School Committee. On his campaign website he exclaims, "Public Service is my life!" He credits a volunteer tour guide position at the State House when he was 16 with......