[FR]: Add option to disable auto updates of AdBlock filter lists on startup

[Dean-Corso]

Brief description of the feature request

Every time I start RSS Guard with enabled AdBlock it gets freezed for few seconds because the AdBlock filter lists getting updated every time. I don't like that and would like to have an option to enable / disable that auto update of AdBlock filter lists. Even I would prefer to update them manually if I want you know. Otherwise RSS Guard should just check the date when it was updated last time and not just update them again & again on every start. Thanks.