SVGHMI: HMI is not speculating on PLC variable update anymore when sending new variable value.

HMI variable cache in JS was changed in advance for more responsive behaviour when updating a HMI tree variable. This was leading to display value different from hmi tree variable in case the expected update did not happen because PLC program did revert it.

<?xml version="1.0" encoding="UTF-8"?>
<BaseParams Name="wxglade_hmi" IEC_Channel="0"/>