Added migration for creating Shortcuts

• Added:
- migration for creating Shortcuts

db/migrate/20200721215336_create_shortcuts.rb

@@ -0,0 +1,12 @@
+class CreateShortcuts < ActiveRecord::Migration[5.2]
+  def change
+    create_table :shortcuts do |t|
+      t.timestamps
+      t.belongs_to :account, foreign_key: { on_delete: :cascade }, null: false
+      t.bigint :shortcut_id, null: false
+      t.string :shortcut_type, null: false, default: ''
+    end
+
+    add_index :shortcuts, [:account_id, :shortcut_id, :shortcut_type], unique: true
+  end
+end