Promotes when all triggered builds succeeded

This works like `DownstreamPassCondition`.
The difference is that, you do not need to specify downstream project names, but it tracks automatically downstream builds triggered from the build.

This is especially useful for the case some of downstream projects are not triggered conditionally, for example by  [Flexible Publisher plugin] (https://wiki.jenkins-ci.org/display/JENKINS/Flexible+Publish+Plugin).

The feature is very alike to `DownstreamPassCondition`, but the implementation is so different that I provided this feature not as an extension for `DownstreamPassCondition`, but as another promotion condition.