Tuto hello world workspace plugin

This is a first draw. any comments are welcomes. Thanks for testings.

The idea is to have just the CMakeLists and the README.md in the master of the repo and this PR in an other branch as the solution of the tutorial.

What do you think about adding comments to explain the role of the main functions in .cpp as turtoriel?

I start by generating a data plugin with the plugin genertor. It could be the base for a new template for the workspace plugins like we discuss during the meeting.