Get downloaded gpx areas
For OsmDataLayer it is possible to get all the Bounds that have been downloaded from the server. This is used in the continuous download plugin to not download the same are multiple times.
GpxLayer does not give you this information because it is merging all GpxData objects into a single object. That prevents the plugin from doing continuous download of gpx traces like it does for osm data. This feature is the most requested feature by #7808 and #7972 .