[FIX] website: allow choosing a body background in full layout

Previous system was strange: you were able to choose a body color but
not a body background when you were in full layout mode.
As transparent colors will soon be able to be chosen by the user, it
makes even more sense to give that possibility as the user can set a
body background pattern and a transparent footer color to let it
appear. Choosing a transparent background image which will be mixed with
the body color is also a common feature.

Also changes boxed layout option to use a white background for the boxed
content (we should maybe give the opportunity to the user to choose that
color instead of using always white).

addons/website/static/src/scss/website.scss

@@ -29,6 +29,10 @@ $-font-numbers: (
         @include media-breakpoint-up(md) {
             padding: 0 7.5%;
         }
+
+        #wrap {
+            background-color: $white;
+        }
     }
 }
 

addons/website/views/website_templates.xml

@@ -468,10 +468,10 @@
             <!-- In a <more/> so that it is on a new line if themes add options before -->
             <more data-depends="">
                 <list string="Body">
-                    <opt string="Full" data-xmlid="" data-enable="option_no_background" data-icon="/website/static/src/img/options/layout-full.png"/>
+                    <opt string="Full" data-xmlid="" data-icon="/website/static/src/img/options/layout-full.png"/>
                     <opt id="option_layout_boxed" string="Boxed" data-xmlid="website.option_layout_boxed_variables" data-icon="/website/static/src/img/options/layout-boxed.png"/>
                 </list>
-                <list string="Background" data-depends="option_layout_boxed">
+                <list string="Background">
                     <opt id="option_no_background" string="None" data-xmlid=""/>
                     <opt string="Choose an image" data-xmlid="website.option_custom_body_image"/>
                     <opt string="Choose a pattern" data-xmlid="website.option_custom_body_image, website.option_custom_body_pattern"/>