improve achievement management and and views

app/models/wow_achievement_category.rb

@@ -4,8 +4,16 @@ class WowAchievementCategory < ApplicationRecord
   extend Mobility
   translates :name
 
+  belongs_to :parent_category, class_name: 'WowAchievementCategory', optional: true
+  has_many :child_categories,
+           class_name: 'WowAchievementCategory',
+           foreign_key: 'parent_category_id',
+           dependent: :nullify,
+           inverse_of: :parent_category
   has_many :wow_achievements, dependent: :destroy
 
   validates :name, presence: true
   validates :category_id, presence: true, uniqueness: true
+
+  scope :base_categories, -> { where(parent_category: nil) }
 end