Added a way to specificy which structures are to be initially displayed (the default being ALL structures displayed) + the loader maintains a list of structure display state, that can be modified continuously + the cache now takes the initial list of structure into account for computing the entry + added methods to change the loaded structure visibility + disabled the alternate loaders (DicomStructureSetLoader2 and friends) + disabled corresponding tests

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