SVGHMI: add support for "reference" and "frame" rectangles to spread-out ovelapping elements.

When HMI become complicated, designer needs to spread-out ovelapping elements
in order to unclutter drawing and facilitate maintenance.

Beremiz's user manual
=====================

Contents:

.. toctree::
   :maxdepth: 2

   install
   start
   edit
   build
   connectors
   debug