Move official samples to a dedicated repository?

I propose to move in the near future the official samples in a dedicated repository *gemoc.official_samples*.

This would make them more visible, give them a status similar to the non-eclipse repos that contain only languages (eg. https://github.com/gemoc/activitydiagram/ or https://github.com/gemoc/petrinet/), and overall reduce the amount of concerns dealt in the big gemoc-studio repo.