Publish does not fail if publishing to graders fails #46
Description
If publishing to graders fails, the publish view will still succeed but with warnings. This is because some graders may have already been published which means that the operation cannot be aborted. To fix this, the Git Manager grader configuration protocol must support rollback to the previous version, so that the versions on already-published graders can be rolled back. In practice, this needs graders to store the previous version of the course as well in case of a rollback.
This is a very rare case that shouldn't really ever happen unless there are bugs elsewhere in the build/configuration process.