Redefine Deco gas creation function: The old function needed a lot of iteration to get through all gases. With the change to define the first gas in PSCR mode as deco gas for calculation (because the actual gas could be not breathable close to surface => deco planing would be based on > 80% nitrogen increasing the deco prediction higher than necessary) the need showed up to somehow define the first gas as deco gas. Instead of manipulating the gas attribute the deco list creation function was changed to create the list based on gas line pointer information instead of index lists. The new function needs less iterations for sorting and is more flexible regarding gas handling.