Keep a copy of converted image at full quality

When a format is converted to png or jpg (as we do for example with tiff files), we should maybe keep a converted copy at the highest quality.

What we currently do

We create two converted copies: medium and small.

What the problem is

Pagedjs cannot display the original tiff file and the converted medium quality image is not good enough for print.

Proposed solution

Keep a third conversion for some formats at full quality.