fix debug button and variable tree generate for actions and transitions in POU instance variable panel
for 'None' type instances(Python POU's, Native, SVGUI, user-defined pou's, etc.) debug button will be disabled. If action or transition instances have opened in instance variable panel,variables from main POU will be loaded. When user press debug button on variable instance in action or transition, instance path to main POU will be used, because all variables of action or transition in instance variable tree belong to main POU.

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. 

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

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.

To be continued.