Code format clean up
Enables the default view to display the 'Invoice' list as per forum thread found here: http://forums.zpanelcp.com/showthread.php?24172-Announcement-ZPanelX-Auto-Billing&p=99619&viewfull=1#post99619
Merge pull request #7 from bobsta63/master

Added default view to load 'Invoices' when initially opening the 'Billing' module in ZPanel.