Basic PDF rendering options

This adds two settings to Configuration > General Settings > Invoice Settings in the Spree backend. The first  allows the default font face to be set and the second provides an option for scaling the logo image down. This can currently be achieved by overriding the templates, but it's useful to allow some basic adjustments to be made from within the admin panel.

I also made the width of the address and line items boxes bump up the the right-hand margin of the PDF. There was roughly a 1/4 inch gap causing the border to not line up with the right justified text.