Fixes #5 and Fixes #6

For Issue 5: Mean Displacement Computation

The measureMeanDisplacement, measureMeanStrain and measureMeanStressIsotropLaw functions have been modified by adding an argument, which is the dimension of the boundary where these values will be computed (should be 1 or 2 in most cases). Test cases have been modified accordingly.

TO BE CHANGED CUSTOM TEST CASE(S): add this argument whenever one of this functions is called in the curveWriter of the test case.

For Issue 6: Possibility for the user to choose the Force displacement export file name

A new parameter curve_writer_output_name has been added to the DamageInfoParser.h file, to eventually give another name to the file where force, displacement, etc are exported. Default file name is still forceouverture.txt, so this commit is transparent if the file name forceouverture.txt is OK for the user.