Rename admin proposal notifications controller

To be consistent with all the other controllers dealing with hidden
content, we use the word "hidden" in the controller class.

app/controllers/admin/hidden_proposal_notifications_controller.rb

@@ -0,0 +1,30 @@
+class Admin::HiddenProposalNotificationsController < Admin::BaseController
+  has_filters %w[without_confirmed_hide all with_confirmed_hide], only: :index
+
+  before_action :load_proposal, only: [:confirm_hide, :restore]
+
+  def index
+    @proposal_notifications = ProposalNotification.only_hidden
+                                                  .send(@current_filter)
+                                                  .order(hidden_at: :desc)
+                                                  .page(params[:page])
+  end
+
+  def confirm_hide
+    @proposal_notification.confirm_hide
+    redirect_with_query_params_to(action: :index)
+  end
+
+  def restore
+    @proposal_notification.restore
+    @proposal_notification.ignore_flag
+    Activity.log(current_user, :restore, @proposal_notification)
+    redirect_with_query_params_to(action: :index)
+  end
+
+  private
+
+    def load_proposal
+      @proposal_notification = ProposalNotification.with_hidden.find(params[:id])
+    end
+end