Title: Process Control on Windows

Description:

Process control primitives are different on POSIX and Windows. We need to add support for the following:

1. Envoy should handle termination signals by the OS
2. Envoy should handle termination signals by the user
3. Envoy should be able to run persistently on the background as a SCM process.

Relevant Links:

Any extra documentation required to understand the issue.

1. SCM
2. Porting Envoy to Windows; A Progress Report - Yechiel Kalmenson & William A. Rowe, Jr., Pivotal
3. Control Handler

cc: @envoyproxy/windows-dev