Tfs build plugin

Based also on the work done by @pombeirP for TeamCity...

At the moment, it works for me...

States are shared with #2166...

Contrary to TeamCity and Jenkins, there is no web api shared by a TFS server :(

That's why I have created 2 projects that use the tfs assemblies for the 2 version of Visual Studio that support a TFS(Git) repository...

PS : Perhaps, you won't be able to build these project because the tfs assemblies are needed (installed with Visual Studio or [Team Explorer for Microsoft Visual Studio](http://www.microsoft.com/en-us/download/details.aspx?id=40776) ) I wonder if I should better build these assemblies and add the dlls in references. What do you think about that?

I get warning here:
Warning	2	'Microsoft.TeamFoundation.Client.TeamFoundationServerFactory' is obsolete: 'The TeamFoundationServerFactory class is obsolete. Use the TfsTeamProjectCollection or TfsConfigurationServer classes to talk to a 2010 or newer Team Foundation Server. In order to talk to a 2005 or 2008 Team Foundation Server use the TfsTeamProjectCollection class. The corresponding factory class for that is the TfsTeamProjectCollectionFactory.'	C:\d\projekty\GitExt\Plugins\BuildServerIntegration\TfsInterop\TfsHelper.cs	68	29	TfsInterop.Vs2012

Is there a reason that you didn't use TfsTeamProjectCollectionFactory?