Better TFVC Support

Add features to VSTS-CLI so that it can work similarly to the Git CLI, but for TFVC. This would enable the possibility of using any editor on any system to easily develop TFVC projects. At the moment TFVC managed projects are a huge pain to use with anything other than Visual Studio IDE on Windows.

If these features are added and improved Visual Studio Code's VSTS extension can latch on top of this to easily add the [missing TFVC features](https://github.com/Microsoft/vsts-vscode/issues/356), and allow easier use with all editors as they would also be able latch on to this command line application.

Some feature examples:
* Committing
* Cloning (+ Workspace management and creation)
* Branching