Consider running multiple classifications in a single task

[marco-c]

Right now the decision task is triggering a classification task for each push, this means some things will have to be recalculated multiple times.
If we find that #564 is not enough, we should try running multiple classifications in a single task.
The single task will be outputting multiple artifacts (one for each push it classified) and will be indexed at multiple paths (one for each push).