Add the first version of migration from LevelDB to RocksDB.
Add the first version of migration from LevelDB to RocksDB.

Signed-off-by: Sergey Shilov <064bbdfaeb89a0bebebfe7b388747a73c8941704@dsr-company.com>

spivachuk/sovrin-node,spivachuk/sovrin-node,spivachuk/sovrin-node,spivachuk/sovrin-node