Clean up git integration implementation class

[andersjaensson]

I think the responsibility between GitCommandHelper and ReadyApiGitIntegration is a bit unclear. A recurring pattern is that in ReadyApiGitIntegration, we get the gitObject from GitCommandHelper, just to send it back in the next method call to GitCommandHelper. That could be handled internally in the GitCommandHelper class.

[shadidchowdhury]

It seems git object is a heavy object containing ref to whole repo. And you probably don't want to recreate it every time. Which means in most of the places we need to move whole implementation to the command helper. And as we discussed this is more of a trade off where do you want to keep the code. I think right now the code is not too clumsy on either side.

[andersjaensson]

Looks good, merging.