Use db schema for tags instead of plugin store and custom fields

db/migrate/20160503205953_create_tags.rb

@@ -0,0 +1,27 @@
+class CreateTags < ActiveRecord::Migration
+  def change
+    create_table :tags do |t|
+      t.string      :name,        null: false
+      t.integer     :topic_count, null: false, default: 0
+      t.timestamps
+    end
+
+    create_table :topic_tags do |t|
+      t.references :topic, null: false
+      t.references :tag,   null: false
+      t.timestamps
+    end
+
+    create_table :tag_users do |t|
+      t.references :tag,  null: false
+      t.references :user, null: false
+      t.integer    :notification_level, null: false
+      t.timestamps
+    end
+
+    add_index :tags, :name, unique: true
+    add_index :topic_tags, [:topic_id, :tag_id], unique: true
+    add_index :tag_users, [:user_id, :tag_id, :notification_level], name: "idx_tag_users_ix1", unique: true
+    add_index :tag_users, [:tag_id, :user_id, :notification_level], name: "idx_tag_users_ix2", unique: true
+  end
+end