Drupal 8.x

Hi Guys
I am trying to alter menu settings section on node form in d8 but unable to create any new fields under that.However if i try to create it outside menu settings it's working fine.Code attached please check and tell what i am doing wrong here.

function Modulename_form_node_form_alter(&$form, FormStateInterface $form_state) {
  $form['menu']['fieldname'] = array(
    '#type' => 'checkbox',
    '#title' => t('Use an icon'),   
    '#tree' => FALSE,   
  );
  }

I've been testing out Drupal 8 to build a REST service, and whenever I try to make a POST I receive this message:
{"error":"number expected"}
I debugged the message and it is thrown because Drupal doesn't find a serialiser even do I have the Serialiser module enabled. I'm making my requests using hal+json, and using Basic Auth, and CORS is responding OK (I can make GET requests without a problem)

I wanted to designate that I'm not a complete newbie, because I first started working with Drupal in 2003. I have developed a handful of sites over the years. But it has been almost four years since I have looked at Drupal or done any kind of web development!

But now I am back and I am about to embark on major web development because I'll be developing 10+ personal and business web sites for myself over the next 1 - 2 months. Thus, I am by no means an expert with Drupal, but I have the basic idea about Drupal from using it in the past.

Hi

During Drupal 8 beta 6 installation I got
«
An AJAX HTTP request terminated abnormally.
Debugging information follows.
Path: http://localhost/8drupal03/core/install.php?langcode=fr&profile=standard...
StatusText: error
ResponseText:
ReadyState: 0
»
That's happended during installation of the help module N° 26/40

I haven't created much content with Drupal as yet and still reading, watching lessons on how it all works.
I had latest version 7 installed and it sat idle doing nothing. Now i have installed beta 8 to try and site is being flooded with spam user registrations.
Is this a coincidence that i have installed 8 and the spam has just started?
If i went back to 7 would this stop or am i too late?
Didnt really want to have to make users use a captcha style rego if possible.
Thanks Heapy

I'm trying to have a tour start automatically in Drupal 8. If I type in ?tour=1 after the path in the url of the browser it works fine. However, trying to do that by adding in ?tour=1 in the routing.yml file and Drupal 8 converts the ? and = to escaped character strings which don't work at all. I looked around but didn't see any reference to what could be put in the routing.yml file get the proper characters to show up in the url being generated. Does anyone know the answer?