Switch to Meson

[peteruithoven]

All Aboard The Meson Future Hype Train explains that elementary OS will be switchting over from CMake to Meson. This probably means we'll also need to update this project, since it's used in the getting started documentation

you can expect our documentation to be updated as soon as the first preview builds of Juno become available to developers.

From: All Aboard The Meson Future Hype Train

I thought it might be interesting to have an issue for discussions and to track progress.

ToDo:

• [ ] Adapt rules file

Also see: https://github.com/elementary/website/issues/1885