Restore filtering investments by milestone status query

This commit makes 3 changes:

1. Extracts a query into a helper for clarity and DRYness

2. Adds a `.where` clause to filter investments based on their
(current) milestone status

3. Fixes a bug where investments would be rendered as many times as
milestones associated to an investment

app/helpers/budget_executions_helper.rb

@@ -0,0 +1,20 @@
+module BudgetExecutionsHelper
+
+  def winner_investments(heading)
+    if params[:status].present?
+      heading.investments
+             .selected
+             .sort_by_ballots
+             .joins(:milestones)
+             .distinct
+             .where('budget_investment_milestones.status_id = ?', params[:status])
+    else
+      heading.investments
+             .selected
+             .sort_by_ballots
+             .joins(:milestones)
+             .distinct
+    end
+  end
+
+end