FEATURE - Moderators can create and manage groups (#10432)

Enabling the moderators_manage_categories_and_groups site setting will allow moderator users to create/manage groups.

* show New Group form to moderators

* Allow moderators to update groups and read logs, where appropriate

* Rename site setting from create -> manage

* improved tests

* Migration should rename old log entries

* Log group changes, even if those changes mean you can no longer see the group

* Slight reshuffle

* RouteTo /g if they no longer have permissions to view group

lib/guardian/category_guardian.rb

@@ -7,7 +7,7 @@ module CategoryGuardian
   def can_create_category?(parent = nil)
     is_admin? ||
     (
-      SiteSetting.moderators_create_categories &&
+      SiteSetting.moderators_manage_categories_and_groups &&
       is_moderator?
     )
   end
@@ -16,7 +16,7 @@ module CategoryGuardian
   def can_edit_category?(category)
     is_admin? ||
     (
-      SiteSetting.moderators_create_categories &&
+      SiteSetting.moderators_manage_categories_and_groups &&
       is_moderator? &&
       can_see_category?(category)
     )

lib/guardian/group_guardian.rb

@@ -3,6 +3,15 @@
 #mixin for all guardian methods dealing with group permissions
 module GroupGuardian
 
+  # Creating Method
+  def can_create_group?
+    is_admin? ||
+    (
+      SiteSetting.moderators_manage_categories_and_groups &&
+      is_moderator?
+    )
+  end
+
   # Edit authority for groups means membership changes only.
   # Automatic groups are not represented in the GROUP_USERS
   # table and thus do not allow membership changes.
@@ -11,7 +20,17 @@ module GroupGuardian
   end
 
   def can_log_group_changes?(group)
-    (is_admin? || group.users.where('group_users.owner').include?(user))
+    can_admin_group?(group) || group.users.where('group_users.owner').include?(user)
+  end
+
+  def can_admin_group?(group)
+    is_admin? ||
+    (
+      SiteSetting.moderators_manage_categories_and_groups &&
+      is_moderator? &&
+      can_see?(group) &&
+      group.id != Group::AUTO_GROUPS[:admins]
+    )
   end
 
   def can_see_group_messages?(group)

lib/site_settings/deprecated_settings.rb

@@ -9,7 +9,8 @@ module SiteSettings::DeprecatedSettings
     ['disable_edit_notifications', 'disable_system_edit_notifications', true, '2.4'],
     ['enable_category_group_review', 'enable_category_group_moderation', true, '2.7'],
     ['newuser_max_images', 'newuser_max_embedded_media', true, '2.7'],
-    ['min_trust_to_post_images', 'min_trust_to_post_embedded_media', true, '2.7']
+    ['min_trust_to_post_images', 'min_trust_to_post_embedded_media', true, '2.7'],
+    ['moderators_create_categories', 'moderators_manage_categories_and_groups', '2.7']
   ]
 
   def setup_deprecated_methods