Display total block size for the block chain

[painbank]

Like BTC has for theirs at: https://blockchain.info/charts/blocks-size

we should have one at https://explorer.lbry.io/charts/blocks-size

Internal Use

Acceptance Criteria

Definition of Done

• [ ] Tested against acceptance criteria
• [ ] Tested against the assumptions of the user story
• [ ] The project builds without errors
• [ ] Unit tests are written and passing
• [ ] Tests on devices/browsers listed in the issue have passed
• [ ] QA performed & issues resolved
• [ ] Refactoring completed
• [ ] Any configuration or build changes documented
• [ ] Documentation updated
• [ ] Peer Code Review performed

[marcdeb1]

This could be added to the block size chart at https://explorer.lbry.io/blocks.