[SofaPython] adding __str__ implementation to Data
[SofaPython] adding __str__ implementation to Data

(cherry picked from commit 2c3d870d6a2c6b5ec18e77fcff957f6601d0675b)

FabienPean/sofa,FabienPean/sofa,FabienPean/sofa,FabienPean/sofa,FabienPean/sofa,FabienPean/sofa,FabienPean/sofa,FabienPean/sofa,FabienPean/sofa,FabienPean/sofa