Adding "Directory.Build.props" and ".editorconfig" about coravel

[jamesmh]

So, TBH the duplicates in csproj files is not an issue at all. But I'm open to starting a simple Directory.Build.props.

Let's not add the sonar analyzer yet though. Would be more appropriate to add that in a separate PR as:

1. This will most likely lead to other code changes I suspect...
2. It's a different intent than just "adding a new Directory.Build.props with existing properties.

LMK once a PR is ready 👍 Thanks!

[iPazooki]

@jamesmh , The pull request with number #346 is now ready. Our next step could be adding <Nullable>enable</Nullable> to identify any possible null exceptions and fix them. However, this won't be an easy task as we need to update some projects as explained in the pull request.

If you are happy with that, I can create another issue for null exception