Added new models to make invoicing more static [PD-870]
Added transaction types to invoices and switched invoice creation to also create InvoiceProducts [PD-870]
Updated tests and added migrations
Reset the forms since I was going about creating invoices incorrectly
Got invoicing in a semi-working state again
Don't create the invoice until an OfflinePurchase has been redeemed
Added tests for static invoice emails
Updated invoice number in invoice emails
Merge pull request #1080 from DirectEmployers/invoicing

Invoicing [PD-870]