Payment info on the invoice, added sale date, billing period, new currencies

[carlosinho]

I needed more info on the invoice and also fixed a couple of issues from here.

These additional details have been added:

• paymentMethod - e.g. "bank transfer"
• bank - "name of bank"
• swift - "bank SWIFT no"
• accountNo - "account no"
• saleDate - these can sometimes be different than issue date, useful to have it
• billingPeriod - useful to indicate the exact billing period the invoice is for (this solves issue #19)

Added two new currencies. This also solves issue #54.

Added the binary and ds_store to gitignore.

Now the invoice looks like this: