Show only active tasks in the overview view

Active tasks are unbilled tasks that are tasks that are either fixed cost
or that have time entries that should be billed.

stoptime.rb

@@ -222,6 +222,12 @@ module StopTime::Models
     def unbilled_tasks
       tasks.where("invoice_id IS NULL").order("name ASC")
     end
+
+    # Returns a list of tasks that are active, i.e. that have not been
+    # billed and are either fixed cost or have some registered time.
+    def active_tasks
+      unbilled_tasks.select { |task| task.fixed_cost? or task.time_entries.present? }
+    end
   end
 
   # == The task class
@@ -755,7 +761,7 @@ module StopTime::Controllers
       @tasks = {}
       @task_count = 0
       Customer.all.each do |customer|
-        tasks = customer.unbilled_tasks.sort_by { |t| t.name }
+        tasks = customer.active_tasks
         @tasks[customer] = tasks
         @task_count += tasks.count
       end