Pulp modularity

[FrostyX]

modularity - check if it works (separate directory for results), ask forman folks (and others) whether this is needed at all, module-hotfixes

[FrostyX]

We got module hotfixes for free with #3383

Building modules probably doesn't work. I think it could be doable but personally, I would vote for not implementing this, keeping all projects with modules in the backend storage. Maybe as one of the latest tasks.

If modularity was implemented through CoprDirs, this would be much easier task. But modularity predates that feature and uses its custom implementation. Relevant issue #1576