add score models

app/models/score.rb

app/models/score_user_category.rb

app/models/user_category.rb

db/migrate/20160222144157_create_scores.rb

db/migrate/20160222144216_create_user_categories.rb

db/migrate/20160222144259_create_score_user_categories.rb

db/seeds.rb

db/seeds/scores.rb

test/fixtures/score_user_categories.yml

test/fixtures/scores.yml

test/fixtures/user_categories.yml

test/models/score_test.rb

test/models/score_user_category_test.rb

test/models/user_category_test.rb