Admin base controller (#1465)

* Add Admin::BaseController to wrap admin area

Extracts the setting of the `admin` layout and verifying that users are admins
to a common base class for the admin/ controllers.

* Add basic coverage for admin/reports and admin/settings controllers

app/controllers/admin/domain_blocks_controller.rb

@@ -1,32 +1,30 @@
 # frozen_string_literal: true
 
-class Admin::DomainBlocksController < ApplicationController
-  before_action :require_admin!
+module Admin
+  class DomainBlocksController < BaseController
+    def index
+      @blocks = DomainBlock.paginate(page: params[:page], per_page: 40)
+    end
 
-  layout 'admin'
+    def new
+      @domain_block = DomainBlock.new
+    end
 
-  def index
-    @blocks = DomainBlock.paginate(page: params[:page], per_page: 40)
-  end
+    def create
+      @domain_block = DomainBlock.new(resource_params)
 
-  def new
-    @domain_block = DomainBlock.new
-  end
+      if @domain_block.save
+        DomainBlockWorker.perform_async(@domain_block.id)
+        redirect_to admin_domain_blocks_path, notice: 'Domain block is now being processed'
+      else
+        render action: :new
+      end
+    end
 
-  def create
-    @domain_block = DomainBlock.new(resource_params)
+    private
 
-    if @domain_block.save
-      DomainBlockWorker.perform_async(@domain_block.id)
-      redirect_to admin_domain_blocks_path, notice: 'Domain block is now being processed'
-    else
-      render action: :new
+    def resource_params
+      params.require(:domain_block).permit(:domain, :severity)
     end
   end
-
-  private
-
-  def resource_params
-    params.require(:domain_block).permit(:domain, :severity)
-  end
 end