[WIP] Add services Install Notes system

I think attaching install notes to services will be more user-friendly.

We often have to know more than just an one line description of the app, this should simplify services installation procedure for users.

This PR is an experiment and a proposition for this moment.

Feel free to let your thinking about this idea and don't hesitate to give me advice for the code flow (methods, file emplacement, tests to be written, UI etc...).

I will attach some screenshot later.

Thanks!