Enabling administrators to revoke VSTS access tokens

Introduced new REST APIs for administrators to centrally revoke Personal Access Tokens (PAT) and JSON Web Tokens (JWT) created by users in their Visual Studio Team Services (VSTS) accounts. Provided a PowerShell script to automate calling these APIs by passing a list of user principal names (UPNs). Announced an automated revocation of potentially impacted tokens for affected customers on August 3, 2018, following email notification to VSTS account admins.