Bump minimum required version of CMake to 3.16 and update CMake SWIG policies

[diegoferigo]

This PR fixes the error due to a bump of the minimum requirement of CMake that is being proposed in #731.

The problem is that recent CMake releases set by default the NEW version of policy CMP0078 that affects the naming of the target and the resulting library. This change breaks the old CMake structure.

In addition to this fix, I also applied the NEW version of policy CMP0086 that allows removing the generic CMAKE_SWIG_FLAGS replacing it with set_property calls.

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P.S. I never used SWIG bindings in a multi-thread application and I'm not sure what's the best way to handle the SWIG flags. It seems that the -threads option that was already enabled is enough to disable the GIL, however as discussed in swig/swig#927 maybe it is not enough and other options should be added in the .i file. Let's keep things as they were before but also keep it in mind in case of multi-threading problems.

[traversaro]

Let's keep things as they were before but also keep it in mind in case of multi-threading problems.

I totally agree!

[diegoferigo]

There are some errors occurring due to the old swig-related CMake policies. I'm not finding the right combination that works in CMake 3.13. Since these checks would have been removed anyway by #731, maybe it's better closing #731 and replacing it entirely with this PR.

@traversaro If after 0e8cdbe the tests pass, feel free to proceed in this way.

[traversaro]

There are some errors occurring due to the old swig-related CMake policies. I'm not finding the right combination that works in CMake 3.13. Since these checks would have been removed anyway by #731, maybe it's better closing #731 and replacing it entirely with this PR.

@traversaro If after 0e8cdbe the tests pass, feel free to proceed in this way.

Thanks, I just updated the Changelog here as well.