Simplify/modify/refactor Blobovniczas

[carpawell]

It becomes hard to maintain its code and it still contains some bugs (at least many could not read object from opened blobovnicza {"path": "9/0/0", "error": "database not open"} was found by me). No performance argumentation is remembered, no open blzs cache understanding has been kept by the devs, etc.

Revise its structure (i mean the blobovniczas tree), understand if it helps to have such a nested structure and if it is much more better than the flat one. Also, does the node have to close databases? Is ~5K open files too big for a production server?