Remove magic indexes

[charleskawczynski]

Magic indexes are used for the dry component of gas_col (0 when using OffsetArrays, 1 with an offset for ordinary Arrays), which complicates the logic. This may be linked to #183, depending on the order things are fixed.

[charleskawczynski]

This was not fixed by #185

[sriharshakandala]

@charleskawczynski , @dennisYatunin , I believe this issue is no longer relevant. I would like to close this unless there are additional comments!

[charleskawczynski]

Magic indices are still used, I wouldn't call this closed.

[sriharshakandala]

We no longer use offset arrays. All indices start from 1.

[charleskawczynski]

That's not the point, the point is that these indices refer to specific gases, and we have to keep track of where they are throughout the code.

[sriharshakandala]

This is done through a dictionary.