Improve exception safety with smart pointers

[elfring]

Would you like to wrap any pointers with the class template “std::unique_ptr”?

Update candidates:

• ConjugueGradient
• Transfo_Mesh3
• Triangles::gibbs

[elfring]

:thought_balloon: Would you like to take the C++ guideline “R.11: Avoid calling new and delete explicitly” better into account?

[prj-]

No.