[REF] website_event_track: improve 'talk proposal' page

RATIONALE

Even will soon gain a major update called Event Online, allowing to better
support full-online events. In order to prepare its merge, preparatory merge
are done to lessen the final diff.

PURPOSE

Prepare Event Online support by providing fixes in registration and event
frontend flows. Also provide a quick back2basic in backend views to prepare
addition of Online sub modules.

SPECIFICATIONS: INTRODUCTION PAGE

Add "a lot of margin". As per original and unique spec. Pupose is to separate
a bit better sponsors and talk proposal.

LINKS

Community PR odoo/odoo#55197
Enterprise PR odoo/enterprise#12113

Task ID-2287372 (Fix Twitter Wall)
Task ID-2309702 (Event Preparatory Merge 4)
Prepares Task ID-2252655 (Main Online Event task)
Prepares Task ID-2283796 (Event B2Basics / Registration Flow)
Prepares Task ID-2299857 (Event Design Review)

addons/website_event_track/views/event_track_templates.xml

@@ -307,7 +307,8 @@
                                 You can add multiple speakers by separating names, emails and phones with commas.
                             </div>
                         </section>
-                        <section id="forms" t-if="event.website_track_proposal">
+                        <section id="forms" class="mb-5"
+                            t-if="event.website_track_proposal">
                             <form class="mt32 js_website_submit_form" t-attf-action="/event/#{event.id}/track_proposal/post" method="post" enctype="multipart/form-data">
                                 <input type="hidden" name="csrf_token" t-att-value="request.csrf_token()"/>
                                 <div class="form-group row">