Multi-currency support: Money + Currency class improvements (#553)

* Money improvements

* Replace all old money usage

app/models/transaction.rb

@@ -1,4 +1,6 @@
 class Transaction < ApplicationRecord
+  include Monetizable
+
   belongs_to :account
   belongs_to :category, optional: true
 
@@ -6,6 +8,12 @@ class Transaction < ApplicationRecord
 
   after_commit :sync_account
 
+  monetize :amount
+
+  scope :inflows, -> { where("amount > 0") }
+  scope :outflows, -> { where("amount < 0") }
+  scope :active, -> { where(excluded: false) }
+
   def self.ransackable_attributes(auth_object = nil)
     %w[name amount date]
   end