wxPython4 sequels: fix exception in connection dialog, force black text in FBD.

- wxPython4 does not have RemoveSizer in API anymore.
- On GTK3 with dark theme default text colour is white, making it unreadable.

<?xml version='1.0' encoding='utf-8'?>
<SVGHMI xmlns:xsd="http://www.w3.org/2001/XMLSchema" WatchdogInitial="10" WatchdogInterval="5" EnableWatchdog="true" Path="{name}"/>