[SofaPython] Restrict the plugin and its dependers to C++11

[guparan]

Python 2.7 is not compatible with C++17 and later

---

This PR:

• builds with SUCCESS for all platforms on the CI.
• does not generate new warnings.
• does not generate new unit test failures.
• does not generate new scene test failures.
• does not break API compatibility.
• is more than 1 week old (or has fast-merge label).

Reviewers will merge only if all these checks are true.

[guparan]

This won't be enough. All bindings made for SofaPython fail when building in C++17.

[1208/2186] Building CXX object modules/SofaExporter/CMakeFiles/SofaExporter.dir/src/SofaExporter/bindings/Binding_STLExporter.cpp.o
FAILED: modules/SofaExporter/CMakeFiles/SofaExporter.dir/src/SofaExporter/bindings/Binding_STLExporter.cpp.o
< ... >
In file included from /media/jenkins/sofa-ci-dev/workspace/sofa-framework/PR-1284/ubuntu_clang-6_options_release/src/modules/SofaExporter/src/SofaExporter/bindings/Binding_STLExporter.cpp:24:
In file included from /media/jenkins/sofa-ci-dev/workspace/sofa-framework/PR-1284/ubuntu_clang-6_options_release/src/modules/SofaExporter/src/SofaExporter/bindings/Binding_STLExporter.h:25:
In file included from /media/jenkins/sofa-ci-dev/workspace/sofa-framework/PR-1284/ubuntu_clang-6_options_release/src/applications/plugins/SofaPython/../SofaPython/PythonMacros.h:29:
In file included from /media/jenkins/sofa-ci-dev/workspace/sofa-framework/PR-1284/ubuntu_clang-6_options_release/src/applications/plugins/SofaPython/../SofaPython/PythonCommon.h:27:
In file included from /usr/include/python2.7/Python.h:88:
/usr/include/python2.7/unicodeobject.h:534:5: error: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
    register PyObject *obj,     /* Object */
    ^~~~~~~~~

See https://ci.inria.fr/sofa-ci-dev/job/sofa-framework/job/PR-1284/CI_CONFIG=ubuntu_clang-6,CI_PLUGINS=options,CI_TYPE=release/2/console

[damienmarchal]

Looks ok soon :)

[guparan]

To be merged ASAP 👍

[hugtalbot]

requested, done!