DB snapshot import/export

[shunsukew]

Description

Part of #49

Entire DB snapshot import/export feature, so that users can share local development blocks/states with others.

Substrate does have db path option --base-path, so without need of implementation at node level, users can choose where to store blockchain data. Also, it is possible to share entire db folder with others.

However, taking snapshot of the exact state of a particular block number, this feature would be useful. Discussion required.

Required Tasks

• Export DB
• Import DB

Estimated done.

{When finished this task?}

Dependencies

{Dependencies issue or PR.}