[#4604] Add basic caching for TimeEntry#cost

db/migrate/004_add_cost_to_time_entries.rb

@@ -0,0 +1,9 @@
+class AddCostToTimeEntries < ActiveRecord::Migration
+  def self.up
+    add_column :time_entries, :cost, :decimal, :precision => 15, :scale => 2
+  end
+
+  def self.down
+    remove_column :time_entries, :cost
+  end
+end