erp5_core: add gadget_image_viewer
A renderJS gadget that implements a simple image viewer with few image manipulation functions (zoom, rotate, and more to come).
It will allow to manipulate images for a better viewing in ERP5, for exemple to inspect an image uploaded in the wrong direction by a customer, or too small to read, without having to download the image.
The image is now accompanied by few manipulation buttons:
And tada:
It also works in the xhtml_style interface:
