VALSO-VALTRANS and VALNA should be merged

[DaveStorkey]

The reason that there are separate VALSO-VALTRANS and VALNA directories under Marine_Val is purely historical (they were developed by different people at different times) and they should be merged. The high level code (and a lot of the low level code) is the same and it is inefficient to have duplicate copies of things. For example, I have improved the data retrieval scripts for VALSO-VALTRANS, but these changes haven't gone into the VALNA versions.

The procedure for merging would be to try to reproduce the standard VALNA plots within VALSO-VALTRANS by copying the relevant scripts over. Once this was achieved, the contents of VALSO-VALTRANS could be moved up a level and the VALSO-VALTRANS directory deleted. The VALNA directory could be kept for a while; I think there are some "optional extras" that Sophia made that we should keep. The README.md file would need to be updated of course.