CMake: switch to use modern way of  setting version
CMake: switch to use modern way of  setting version

Use the modern project function signature (see https://cmake.org/cmake/help/v3.5/command/project.html) 
to set the version of the project there, without the need of manually setting the <project>_VERSION variable. 
This commits also: 
* Bump the version to 3.0.100 
* Use PROJECT_NAME to define VARS_PREFIX, and avoid duplication
robotology/idyntree,robotology/idyntree,robotology/idyntree,robotology/idyntree,robotology/idyntree