when a data source is requested but does not exist, allow the engine the opportunity to add it by reimplementing dataSourceRequested(const QStringwhen a data source is requested but does not exist, allow the engine the opportunity to add it by reimplementing dataSourceRequested(const QString&).

this makes it trivial to add timezones to the time engine, rss feeds to an rss engine, weather stations to a weather engine or hardware data to solid engines.). this makes it trivial to add timezones to the time engine, rss feeds to an rss engine, weather stations to a weather engine or hardware data to solid engines.