Bug correctic in the corTsgMedian function and linear

La carte géographique affiche désormais le tracet du bateau entre le limites temporelle de l'Axe 1. 
Si l'axe 1 est zoomé, la carte l'est aussi.

add missing_value field to tsg_ncvar.csv for <var>_QC variables
add autonan mode with FillValue_ attribut
correct bug on last selected display QC, tsg structure wasn't saved before display QC
add option/preference mode for autoloading data and use .mat file in prefdir to save user preferences
add tag to handle axes but don't use it

Add frequency conversion and description from TsgRaw but algorithm still comment

Une seule fonction pour la gestion des codes