Added empty project for pub integration.
Extend StdIOService to take a working directory.

This will be required for pub support.
Extract GetSdkPath out into DartVS.Common.

We'll need this for Pub integration too.
Extract remote Sdk Location into constant.
Added a TODO about a multi-threading/race condition.
Removed unused cancellation token.

It's misleading to take a cancellation token if it's not used. We can
add this back in if we add support for it.
Return process exit code from StdIOService.
Created basic "pub get" wrapper.