SVGHMI: Add "lang" permament persistent HMI_LOCAL variable to reflect selected language, apply stored language choice at startup and make it always subscribed to a pseudo widget (as for hearbeat) that apply language choice when it changes.

<?xml version='1.0' encoding='utf-8'?>
<BeremizRoot xmlns:xsd="http://www.w3.org/2001/XMLSchema" URI_location="PYRO://127.0.0.1:61284">
  <TargetType/>
  <Libraries Enable_SVGHMI_Library="true"/>
</BeremizRoot>