[FIX] gamification: avoid sending reports for non-reported challenges
[IMP] website: refactor website_image controller (and placeholder), move to model to make it reusable

It is "almost" reusable because it still depends on the global `request` variable,
this could be solved by making it an explicit parameter.
[FIX] website_forum: fix controllers losing paging and query params, allow to see own profile even without karma, add avatar controller to make the images public
[REV] Revert lazy sitemap