[IMP] web: kanban content container

The 'new' (read: the classes not in the 'compatibility layer section')
classes of the kanban views did not allow to cleanly separate an image
header from a content container.

This commit adds such a container, allowing a very simple layout that
should work all the time for a typical 'card with left image and right
content layout':
```xml
<div class="o_kanban_record oe_kanban_global_click o_kanban_record_has_image_fill">
  <field class="o_kanban_image_fill_left" name="image_128"
         widget="image"
         options="{'zoom': true, 'background': true, 'preventClicks': false}"/>
  <div class="o_kanban_record_details">
    <div class="o_kanban_record_top">
      <div class="o_kanban_record_headings">
        <strong class="o_kanban_record_title">
          <field name="x_name"/>
        </strong>
      </div>
    </div>
    <div class="o_kanban_record_body">
      <!-- some fields here (e.g. tags,...) -->
    </div>
    <div class="o_kanban_record_bottom">
      <div class="oe_kanban_bottom_left">
        <!-- some fields here (e.g. kanban status,...) -->
      </div>
      <div class="oe_kanban_bottom_right">
        <!-- some fields here (e.g. user image,...)-->
      </div>
    </div>
  </div>
</div>
```

Before this commit, the absence of a container for the right side meant
that the top/body/bottom were flex-growed in a flex-direction: row
element, appearing as 3 columns instead of rows.

addons/web/static/src/scss/kanban_view.scss

@@ -58,6 +58,13 @@
             width: $o-kanban-color-border-width;
         }
 
+        .o_kanban_record_details {
+            display: flex;
+            flex-direction: column;
+            justify-content: space-between;
+            width: 100%,
+        }
+
         // Inner Sections
         .o_kanban_record_top, .o_kanban_record_body  {
             margin-bottom: $o-kanban-inner-hmargin;