Create vcs 'aliased' command proxy

[marcinkuzminski]

The general idea, is to hae vcs proxy & detect an scm to issue basic commands to GIT or HG so it's easier to work with scm
for example issuing vcs pull should detect a repo and issue hg pull for mercurial, or git pull for git.

Raise exception on more than one scm detected.

This needs a little brainstorming, and good set of defaults but i think it can be done quickly.

Good basic source: https://github.com/sympy/sympy/wiki/Git-hg-rosetta-stone