Default to disabled debug log on Q_LOGGING_CATEGORY calls

This removes the need to call QLoggingCategory::setFilterRules()
in the program code to default to disabled debug type log
without any other settings.
The latter has disadvantages, as it shadows any settings done
in qtlogging.ini config files by the user
(e.g. via kdebugsettings), thus enabling runtime control only
via QT_LOGGING_CONF/QT_LOGGING_RULES, which is not that
comfortable with lots of categories.

Also use ECMQtDeclareLoggingCategory for less manual code