Feature 5516

Code a system of image resizing on-demand. The images are resized at the asked size if not already done and save the result into a cache.
For doing, a two stages system is coded:
* a JSL tag in ViewGenerator to render an image and that take into account size parameters and size properties to refine the URL of the image in order to target its resized version.
* an image resizing processor triggered when the image is accessed in order to deliver it to the end-user.

For instance, only the users' avatar and the images in an XML form are taken in charge by the dynamic image resizing.