SVGHMI: Fixes UI lifecycle problems

Was sometime showing HMI tree of previously closed project : no more module globals to store hmi tree.
C++ dead object exceptions happened when re-opening SVGHMI UI or building after close of UI.

Beremiz's user manual
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Contents:

.. toctree::
   :maxdepth: 2

   install
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   edit
   build
   connectors
   debug