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

* Money improvements

* Replace all old money usage

app/models/account.rb

@@ -1,5 +1,6 @@
 class Account < ApplicationRecord
   include Syncable
+  include Monetizable
 
   validates :family, presence: true
 
@@ -9,6 +10,8 @@ class Account < ApplicationRecord
   has_many :valuations
   has_many :transactions
 
+  monetize :balance
+
   enum :status, { ok: "ok", syncing: "syncing", error: "error" }, validate: true
 
   scope :active, -> { where(is_active: true) }