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

db/migrate/20200810220841_rename_moderators_create_categories_setting.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+class RenameModeratorsCreateCategoriesSetting < ActiveRecord::Migration[6.0]
+  def up
+    execute "UPDATE site_settings SET name = 'moderators_manage_categories_and_groups' WHERE name = 'moderators_create_categories'"
+    execute "UPDATE user_histories SET subject = 'moderators_manage_categories_and_groups' WHERE subject = 'moderators_create_categories'"
+  end
+
+  def down
+    execute "UPDATE site_settings SET name = 'moderators_create_categories' WHERE name = 'moderators_manage_categories_and_groups'"
+    execute "UPDATE user_histories SET subject = 'moderators_create_categories' WHERE subject = 'moderators_manage_categories_and_groups'"
+  end
+end