Allow updating the status of notifications

You can update the same "notifications" section that we allow you to
update in "my account".

This "subscriptions" section differs from the "my account" section
because we do not need to be logged in to update the status of the
notifications.

app/controllers/subscriptions_controller.rb

@@ -5,6 +5,12 @@ class SubscriptionsController < ApplicationController
   def edit
   end
 
+  def update
+    @user.update!(subscriptions_params)
+    redirect_to edit_subscriptions_path(token: @user.subscriptions_token),
+                notice: t("flash.actions.save_changes.notice")
+  end
+
   private
 
     def set_user
@@ -14,4 +20,12 @@ class SubscriptionsController < ApplicationController
                 current_user || raise(CanCan::AccessDenied)
               end
     end
+
+    def subscriptions_params
+      params.require(:user).permit(allowed_params)
+    end
+
+    def allowed_params
+      [:email_on_comment, :email_on_comment_reply, :email_on_direct_message, :email_digest, :newsletter]
+    end
 end