Updating spacing on invoices/models.py
Replacing Invoice.estimate with Invoice.is_tendered
Deleting Invoice.estimate and adding Invoice.is_void
New method Invoice.get_status()

- Uses status_detail and is_void to determine status

- Returns unicode value
New method Invoice.void

- Voids an invoice
Overwriting Invoice manager to return non-void invoices
Adding "Void invoice" feature
Removing "import get_setting" in invoices/views.py
Adding 2 new methods to query invoice records in InvoiceManager

- These 2 new methods have access to all invoice records, including void invoices.
Adding new Invoice method unvoid.  It un-voids an invoice; makes it active.

- Toggling an invoice from void to active and back is a feature.
Removing "import include" from invoices/urls.py
Adding unvoid feature