Create nested objects

This is similar in idea with nested tags, but for objects. This open up implementations like subtasking.

E.g. "javascript/promise" and "household/promise" are different objects. In this case, "household" and "javascript" are objects, not types nor tags. So they can contain blocks too. Also they could potentially be different types too. The backlinks are objects that references "household" and "household/*". This is more flexible than nested tags which can only collect other tagged objects.

An implementation could be that objects can mark field(s) as parent. This is potentially nasty due to the recursion that might occur, so there might need to be cyclic dependency detection during creation.