Add repository, tag and other parameters to image

In the current way to get images, there is no way to get the repository or the tag of the image. The only unique identifier is the docker_id.

I think that it is a good idea to base functions on it and not having different kind of data in the id attribute of the class. Now the id can't be a image name anymore.

I pull-requested this branch because it is necessary to have separate functions for Container and Image.