Quentin 06/07/2021: update Python lib to read NetCDF4 groups and adapt KTEST to the new read functions + cleaning

Quentin 06/05/2021: Python lib update. Add AVION and AVIONZ time series; correction of reading from netcdf group;
read MASK variables; improve date printing; add colorbar formatlabel; remove contour label (to debug); add streamline plot

Quentin 19/04/2021: minor python plot adapt size of png files and correction of arguments for xx and yy axes for XY lines plot

Quentin 16/04/2021: add reading of netcdf group in addition to individual variables for time series budget and TSERIES/XTSERIES/ZTSERIES

Quentin 16/04/2021: adapt visu python KTEST to display command instead of (convert + evince) for portability