Removed unused file.
Updated the test settings to use crispy forms and django guardian.
Added factories for User, Invoice and InvoiceItem.
Added django guardian to the settings.
Added the invoice view permission.
Added 3 tests for invoices view permission.
Added the permission check on InvoiceDetail view.
wightinvoices has nothing to do in the INSTALLED_APPS.
Merge remote-tracking branch 'origin/develop'