SVGHMI: add "unsubscribable" property to widgets in order to generalize what already happens for jump buttons.
In most cases jump buttons do not really subscribe to pointed HMI variable, path is given as a relative page jump path. When widget.unsubscribable is set to true, no subscription is made on page switch, but still offset is updated.
This fixes bug happening on relative jump buttons without "disabled" element where offset did not change on relative page switch.

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Project overview

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In order to target the widest possible range of programmable devices and keep efficient, Beremiz use C code as an intermediate language. 

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To be executed, C needs to be compiled. `GCC <http://gcc.gnu.org>`_ serve that purpose perfectly.

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PLC program is expressed in languages defined in IEC-61131, including graphical languages. Thanks to PLCopen TC2, those graphical languages have a standardised representation, in XML.

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To be continued.