fix deprecation warnings about accessing properties m_x, m_y of wxKeyEvent

/home/beremiz/beremiz/controls/PouInstanceVariablesPanel.py:354: wxPyDeprecationWarning: Accessing deprecated property.
event.m_x = size.width / 2

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[TOPOLOGY]

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NetName=None

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Nodes=0x01

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Node64Present=0x01

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Node64Name=micromod

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Node64DCFName=PEAK MicroMod.eds

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EDSBaseName=eds