Option to use results from restart file for aggregated variables (linked to issue #727)

It would be nice to have an option when there is in both the PREVIOUS COMPUTATION FILE (restart file) and in VARIABLES FOR GRAPHIC PRINTOUT aggregated variables like MAXZ, TMXZ, MAXV or TMXV to take into account results in the PREVIOUS COMPUTATION FILE (or not).

By default, it could be to take into account the results in the restart file (by experience, it is the user expected behaviour).

This issue is linked with #727