Results 1 issues of ZS Zhang

Hi, I'm not pretty sure, but according to memory-check by valgrind, it seems that this line might be a possible source of memory leak: [here](https://github.com/andre-martins/AD3/blob/22131c7457614dd159546500cd1a0fd8cdf2d282/ad3/GenericFactor.cpp#L437) Since `active_set_[k]` and `configuration` are...