Support Blockchain Reorganization

[eukreign]

• [ ] implement support for detecing reorganizations and recovering
  • [x] rewind the headers
  • [ ] undo any transactions
• [x] unit tests for rewinding headers
• [ ] unit tests for dropping transactions that happened on removed blocks
• [x] integration tests using generate and invalidateblock commands

how do reorgs affect files you have on disk and claims you paid for?

[eukreign]

@hackrush01 implement this method: https://github.com/lbryio/torba/blob/7a8c2fc98ba31751ec9262ab4adcefe4f6335a9e/torba/client/basedatabase.py#L334

[eukreign]

this is the tests for the header rewinding, transaction rewinding would be similar / build on this test: https://github.com/lbryio/torba/blob/master/tests/client_tests/integration/test_blockchain_reorganization.py

[hackrush01]

This comment will be updated with progress

• [ ] Write test to reproduce the issue (2 points, by conservative estimate)