RSA : Add the possibility to affect a sign to the result of a Quadratic combination

[Nader_ASSAF]

In order to have correct and usable results in the non-linear calculation of cases of pseudostatic forces, I propose to give the user the possibility to choose to assign the sign of a pseudostatic case to the results of the quadratic combination (in the same way as the seismic quadratic calculation).

Having a sign for the quadratic results will help to have a correct result for compression and traction in the walls and for constraints in the foundation.

Thanks in advance.

Nader ASSAF.