enhance: transparent/margin section via Container

[wesleyboar]

Overview

Add "Section" (no color) to Container options.

Related

• assists with WP-588

Changes

• changed DJANGOCMS_BOOTSTRAP4_GRID_CONTAINERS setting

Testing

1. Create a "Container + Section (…)".
   ^{i.e. container o-section}
2. Create a "Fluid container + Section (…)".
   ^{i.e. container-fluid o-section}
3. Create a "Section (…)".
   ^{i.e. o-section}
4. Verify each is created with expected classes.

UI

render	select