Thumbnail generation + layout

[Boyan Sheytanov]

Hi Jacob,

Just to note that thumbnails for Decapod will not be square-sized, as
they should represent a spread of pages or a single page. So a default
size of 256x256 would not look good. Auto-scaling also does not seem
the best option to me. Apart from wasting resources, it doesn't look
well with the image reorderer that the thumbnail browser in Decapod is
built upon (when you drag a thumbnail that is auto-scaled, a ghost
image with the original size is shown).

On first thought, our best option is to provide image cropping and
scaling API in Kettle, as it might be needed by Decapod, Fluid Engage
and other projects. If it is customizable enough and simple to use, I
don't imagine it would be a burden for institutions (as they need to
deploy Kettle anyway).

Greetings,

Boyan