adds budget's groups & headings to admin

app/controllers/admin/budget_groups_controller.rb

@@ -0,0 +1,15 @@
+class Admin::BudgetGroupsController < Admin::BaseController
+
+  def create
+    @budget = Budget.find params[:budget_id]
+    @budget.groups.create(budget_group_params)
+    @groups = @budget.groups.includes(:headings)
+  end
+
+  private
+
+    def budget_group_params
+      params.require(:budget_group).permit(:name)
+    end
+
+end