Downloaded Invoice should have fixed size

[fazzaamiarso]

Currently to download an Invoice, we calculate the rendered ref element size and scale to fit the paper size. The problem is when the screen is smaller, the invoice become narrower according to how it appear in the screen, but still scaled to fit the paper size.

What we need is to have the downloaded invoice have the same size in any screen width, doesn't matter how it appear when rendered. The function responsible for the calculation is in src/utils/invoice.