Add the ability to list invoices.

Closes #10.
Reorder switch statement in index.php
Add the ability to view an invoice in the system.

Closes #11.
Add the ability to edit an invoice in the system.

Closes #12.
Add the ability to create an invoice in the system.

Closes #15.
Set `address2` to default to NULL
Rename `cust_id` column to `clid` in invoices table
Merge branch 'master' into demo

Conflicts:
	app/includes/home.inc.php