* Wounded Arizona ex-lawmaker says "enough" * Group seeks "common-sense" solutions to curb violence * Giffords initiative aims to raise funds, challenge NRA By Susan Heavey WASHINGTON, Jan 8 (Reuters) - Former U.S. Representative Gabrielle Giffords, who was severely wounded two years ago in an Arizona shooting, is launching a group aimed at curbing gun violence and raising enough money to challenge the well-funded gun lobby.