Better error log in fetch failure callback + timeout 600sec in OrthancRestApiCommand + guard against dead controller access in PanSceneTracker + relaxed DicomStructureSet AddReferenceSlice method to accept extraneous adds of the same slice (while trying to understand how it happens in the first place)

#define ORTHANC_OVERRIDE
#define ORTHANC_STONE_DEFINE_EMPTY_MESSAGE(FILE, LINE, NAME) class NAME : public ::OrthancStone::IMessage {};