[dot] expandes cuboids type to mark which parts of dot_T%gse are sorted accordinf SFC
[dot] dummy routine for finding grid by its SFC id
[dot] dummy routine for sorting list of grid containers by their SFC id
renamed grid_container%init to init_gc to avoid confusion
added SFC_id to grid_container, keep it up to date
creates sortable list of pointers to grid containers
moved cg_list_T%sort_SFC to cg_list_balance_T
[cg_list_balance] fully functional sort_SFC, that sorts the linked list of grid containers according to their SFC_id
cosmetics
Merge commit '628f931' into cg_add_sorted
Merge branch 'cg_add_sorted' into SFC_neighbors
[dot] update dot_T%gse(:)%sorted