Revert "A little bit of refactoring and reorganization on the buildsets." Revert "A little bit of refactoring and reorganization on the buildsets. Simplifies the buildset creation a lot.

If it does not fix the bug, we will have to create some kind of "restructuring" state for the project or just add the new tree to the project when it's ready."

Fixes a crash on startup when a buildset has more than one items. The
commit needed to be reworked anyway. I'm going to do that tonight.