Cli skeleton

This provides a skeleton of the CLI. It is creating a `ProjectData` object and that's all for now.
Next steps shall include setup of processes, calling global assembly, and solving the resulting system of linear equations.
No you don't. It's just that the version number is something that Olaf is mentioning *everytime* we talk about OGS-6.
How is the version number currently determined when the ```--version``` flag is used? Are we currently in some kind of *beta*-stage? (That's what I am currently doing with the DataExplorer, the title bar says OGS 6.0.0 beta, just so some kind of proper number is displayed and everyone is happy)