GOLEM/golem_activity_queue/views/golem_activity_views.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
Copyright 2018 Fabien Bourgeois <fabien@yaltik.com>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
-->

<odoo>
  <data>
    <record id="golem_activity_form_inherit_golem_activity_queue"
            model="ir.ui.view">
    <field name="name">Add the queue registration button to activity form</field>
    <field name="model">golem.activity</field>
    <field name="inherit_id" ref="golem_activity.golem_activity_form" />
    <field name="arch" type="xml">
      <xpath expr="//field[@name='is_overbooked']" position="after">
        <field name="queue_allowed"/>
      </xpath>
      <xpath expr="//field[@name='activity_registration_ids']" position="after">
        <button class="oe_highlight" name="queue_register" string="Register in the queue"  type="object"/>
      </xpath>
    </field>
  </record>

  <record model="ir.ui.view" id="wizard_form_view">
    <field name="name">queuepopup.form</field>
    <field name="model">golem.queuepopup</field>
    <field name="type">form</field>
    <field name="arch" type="xml">
      <form string="Add motif">
        <footer>
          <button class="oe_highlight" name="queueYes" string="Yes"  type="object"/>
          <button class="oe_highlight" name="queueNo" string="No"  type="object"/>
        </footer>
      </form>
    </field>
  </record>
</data>
</odoo>