- Remove inMainChain from block nodes since that can now be efficiently
  determined by using the chain view
- Track the best chain via a chain view instead of a single block node
  - Use the tip of the best chain view everywhere bestNode was used
  - Update chain view tip instead of updating best node
- Change reorg logic to use more efficient chain view fork finding logic
- Change block locator code over to use more efficient chain view logic
  - Remove now unused block-index-based block locator code
  - Move BlockLocator definition to chain.go
  - Move BlockLocatorFromHash and LatestBlockLocator to chain.go
    - Update both to use more efficient chain view logic
- Rework IsCheckpointCandidate to use block index and chain view
- Optimize MainChainHasBlock to use chain view instead of hitting db
  - Move to chain.go since it no longer involves database I/O
  - Removed error return since it can no longer fail
- Optimize BlockHeightByHash to use chain view instead of hitting db
  - Move to chain.go since it no longer involves database I/O
  - Removed error return since it can no longer fail
- Optimize BlockHashByHeight to use chain view instead of hitting db
  - Move to chain.go since it no longer involves database I/O
  - Removed error return since it can no longer fail
- Optimize HeightRange to use chain view instead of hitting db
  - Move to chain.go since it no longer involves database I/O
- Optimize BlockByHeight to use chain view for main chain check
- Optimize BlockByHash to use chain view for main chain check