Account:: namespace simplifications and cleanup (#2110)

* Flatten Holding model

* Flatten balance model

* Entries domain renames

* Fix valuations reference

* Fix trades stream

* Fix brakeman warnings

* Fix tests

* Replace existing entryable type references in DB

app/models/trade.rb

@@ -0,0 +1,21 @@
+class Trade < ApplicationRecord
+  include Entryable, Monetizable
+
+  monetize :price
+
+  belongs_to :security
+
+  validates :qty, presence: true
+  validates :price, :currency, presence: true
+
+  def unrealized_gain_loss
+    return nil if qty.negative?
+    current_price = security.current_price
+    return nil if current_price.nil?
+
+    current_value = current_price * qty.abs
+    cost_basis = price_money * qty.abs
+
+    Trend.new(current: current_value, previous: cost_basis)
+  end
+end