Fix Invoice Batch Job Controller.
Fix reminder batch jobs.
Do not fails in ReminderBatchJob#to_s if created_at is nil.
Update CHANGELOG.
Add config files for zeus.
Reorganize reminder methods in Invoice.
Show reminder due date on reminder letters.
Update CHANGELOG.
Merge branch 'staging'

Conflicts:
	CHANGELOG
	app/controllers/reminder_batch_jobs_controller.rb
	app/models/invoice.rb