Provide info if MR is approvable in API response

Created by: Great-Antique

We have own integration system and one of the steps in our integration work flow is a creating build from MR last version and a testing it. So we need to know is MR is approvable or has a merging conflicts to start or not to start a build creating and/or change issue status.

Maybe is it possible to checkout locally MR? Like from github https://gist.github.com/piscisaureus/3342247