[model] logic for sorting and validations
[view] sorting & custom errors
[migrate] add seat number to enrollments
[spec/feature] enrollment spec both side
[route] add routes for class group enrollments
[controller] add class group enrollments controller that inherit for polymorhic enrollments controller
[factory] sequence name
[locale]
[coffee] add add_sortable function
Merge branch 'master' of github.com:Genshin/gaku into seat_number
[model] add few checks in enrollment model
[spec/model] custom validation for semester overlapping
[controller] set_enrollmentable
[spec/feature] fix
[spec/request] fix
[spec/routing] fix
[model] fix
[locale] add semester overlapping message to locales
[specs] DRY semester assignment
[model] bug fix. t instead of I18n.t