SVGHMI: better handling of page switch fade-out.

- In cases or relative jump to current page, page was keeping black after switch.
- Now keep track of undergoing page switch without comparing subscribed page to visible page.

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<?xml version="1.0" encoding="UTF-8"?>

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<BeremizRoot URI_location="LOCAL://">

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  <TargetType/>

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</BeremizRoot>