Azure AD has been updated with a new configuration blade called Organizational Relationships.
This new configuration blade is the new location to manage guest users permissions and invitations
You now have access to a comprehensive list of users from external organizations (guest) with the option (as you already from the users list) to create a new guest
By the way the invitation email has been also updated to use your Azure Company Branding (see https://docs.microsoft.com/en-us/azure/active-directory/fundamentals/customize-branding if you need to know more about)
You can also new identity providers (at this time only Google is available but I’m sure more will come)
NOTE you do not need to add new providers for users using either Microsoft Account (MSA) or Microsoft Corporate account (Azure AD/Office 365)