Implement Delta API to mirror DCL data

[ashcherbakov]

In order to mirror the DCL data in asynchronous mode, a Delta API needs to be designed and implemented, so that all changes between A and B can be get.

Open questions:

• Should it be time based or blockchain height (block number) bases?
• Do we need a state proof (a possibility to work with untrusted nodes)?
• Should we return all changes (all transaction types), or filter by a transaction type (for example return only changed ModelVersions)?
• A need for pagination for huge deltas?

[osbornchan-apple]

• Should it be time based or blockchain height (block number) bases?
  "time based" is preferred.
• Should we return all changes (all transaction types), or filter by a transaction type (for example return only changed ModelVersions)?
  "filter by a transaction type" is needed.
• A need for pagination for huge deltas?
  Yes. pagination is needed.