Fixed client-cache problem: now we use a unique name each time we regenerate the gallery.

- sort by last log in
- image cropping
- limiting the number of rows in the gallery
- minor reorganisation of menus and configuration page

Bug fix:
- blank lines at the end of the gallery
- error when gallery has no users

This fix the following issues:
Patch 137202
Support request 152437
Support request 144288
Support request 150083
Support request 122389
Bug 137267
Feature request 218964
Feature request 152432 (partial)
Feature request 171341 (partial)
Bug 173252