When some builds inside of MultiJob build tree fail, we have two options (after fixing the issues):
1. Restart everything from the top of the tree — takes too much time
2. Manually start all broken builds — requires too much attention from the user

I want to introduce a new feature: resume build. When resume id sone, all sub-builds, which were successfully built, are not rebuild. Only those builds, which were broken (and those, which were not built at all) are built in the correct order, preserving previously set parameters.