Proper FeedCache support and other fixes

* Redefined primary key in `FeedCache`
* Added `block_num` column to `FeedCache`
* `FeedCache` is now build during initial sync
* Batch insert added to `FeedCache` following batch
  insert scheme from other classes
* Added `setup_shared_db_access` method to class
  `DbAdapterHolder`, after initial sync all classes basing
  on this class will use single db connection to use transaction
  properly in `listen` method