[tfsbuild.vnext] Add a NPM cache mirror on Hosted Build Controller's Network

Ability to set build priority

Allow Enable/Disable build (similar to XAML builds)

Make it possible to set time zone on TFS Online (build) server

Trigger build when pushing tag to git

Being able to use the short commit ID to Build from previous commit

Build support for external submodules that require authentication

Allow Build Agent Capabilities to be used through Environment Variables

Allow TFS build to depend on multiple repositories

Enable Continuous Integration Path Filters for Github