Changed matrix <-> fracture test when adding NNC information to discard all NNC with at least one fracture cell (i.e. global_index >= nx*ny*nz)
Added functions nnc_info_get_self_vector() and nnc_info_get_self_index_list() to get nnc connections to the same grid as the cell is part of
Added _get_lgr_name() which takes lgr_nr as input
Added nnc_info_iget_vector() which takes an index in the space [0,nnc_info_get_size())
Added some basic nnc use information