ERT-723: Removed the LARGE_CELL_MALLOC flag

Previously the cells could be allocated either as list of pointers to
cells, or as one large chunk of memory. There was a quite significant
performance hit from creating and destroying the cells individually
, therefor only the 'one continuous chunk' is supported.
ERT-723: Added nnc_vector copy() and equal()
ERT-723: Added nnc_info copy() and equal()
ERT-723: Added ecl_coarse_cell_equal()
ERT-723: Added ecl_grid_alloc_copy()