Support VS 2019

[tstivers1990]

I've updated the project to support VS 19. You may want to give it a look over as I'm not familiar with extension development and mostly just copied your code to get the desired result. I tested it in the latest version of VS 19 and it worked as expected with the settings pages etc working.

I got the lib DLLs from C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\Common7\IDE\CommonExtensions\Microsoft\TeamFoundation\Team Explorer

I didn't bump the version. I figure that's best left up to you.

Summary of Changes:

• Add CommitFormatter.TeamFoundation.16.0 project
• Add lib/16.0 DLLs
• Reference new project from solution
• Reference new project from source.extension.vsixmanifest
• Update version ranges in source.extension.vsixmanifest

Closes #13

[ahoisl]

I can confirm that the changes make the extension work in VS 2019 again, great job @tstivers1990 !