Avoid using Project parameter at the Client constructor

[pbelousov]

Hi,

Azure DevOps supports working with different Team Projects. And it looks like your Client type should not ask to provide Project parameter at the constructor (NewClient method) because there are [several APIs|https://docs.microsoft.com/en-us/rest/api/azure/devops/core/] which don't require projects at all. And it looks more consistent to pass Project only when you want to work with exact one project.

So right now Client describes a class for working with just one project but maybe it would be useful to have a separate type which will work with Azure DevOps in general and will be able to return your current "project" client.

Thank you in advance!