API v1 financial_transactions endpoints (#627)

app/serializers/financial_transaction_serializer.rb

@@ -0,0 +1,13 @@
+class FinancialTransactionSerializer < ActiveModel::Serializer
+  include ApplicationHelper
+
+  attributes :id, :user_id, :user_name, :amount, :note, :created_at
+
+  def user_name
+    show_user object.user
+  end
+
+  def amount
+    object.amount.to_f
+  end
+end