auv_nav: Naming of output folder (json_renav_xxxxx) makes it cumberson to handle multiple versions of it

[adrian-bodenmann]

Naming of output folder (json_renav_xxxxx) makes it cumberson to handle multiple versions of it, as well as using the nav solutin after changing inputs and meaning to overwrite old results. Depending on the change in input data json_renav_xxxxx folder may or may not change names, but almost impossible to predict

Suggestion: justp call the folder "nav".
Put parsed and processed data into that folder