Bug #901: add tags, activity, theme, location.area search key on all models
Bug #901: search offers with organization
Bug #871: link tags, themes and sectors to global search
Bug #928: add descritpion field to offer admin list
Fix broken logout link in right menu
Fix "View on site" link for offers
Fix bug #970: hide "Partenaires" tab if empty
Bug #972: show added value on provider presentation tab