Early detect when a package provided by the robotology-superbuild installed with conda dependencies is also present in the conda environment itself

[traversaro]

As the conda binaries for projects built by the robotology-superuild see an increase of usage (for example yarp, idyntree or casadi) it happens more and more that the users experience problems as they try to build the robotology-superbuild in an environment in which some package built by the robotology-superbuild is already present. What is particularly tricky is that users sometimes did not installed the package explicitly, but it was installed as a transitive dependencies.

In this issue I would like to discuss how to mitigate this problem. For example, we could have a check in the robotology-superbuild that lists the conda packages present in the environment, and check for conflicts to either raise an error or a visible warning (probably an error may be the only way for users to actually check it out, but I am a bit afraid it may be more harmful then beneficial).