add unique index for registrations (user, league)
add unique index for registrations (user, league)

rdonnelly/ultimate-league-app,a2ultimate/ultimate-league-app,rdonnelly/ultimate-league-app,rdonnelly/ultimate-league-app,a2ultimate/ultimate-league-app,a2ultimate/ultimate-league-app,a2ultimate/ultimate-league-app,rdonnelly/ultimate-league-app