Add a module to plot user provided data in "linear plots"

[joernu76]

For quick analysis, it would be useful to, e.g., compare model H2O against FISH H2O after the flight. The linear plot feature allows extraction of H2O along the flightpath, but one cannot, currently, can add user provided data.

This issue would add a widget to allow adding user provided data. Supported data formats would need to be defined, but i would restrict this to CF-compliant 1-D netCDF files. Some simple tools to adjust the time axis need to be present (i.e. shift and stretch).

[ReimarBauer]

This likly is solved by implementing https://open-mss.github.io/develop/GSOC/figure_objects