Relaying BTC block headers

The relayer began as a fork of Babylon's Vigilante. A large portion of Vigilante's original functionality has been removed; what is left is mainly the reporter, which is responsible for relaying block headers and checkpoints. The reporter itself was also stripped of some of its main components, namely the code dealing with extracting and forwarding checkpoints, which leaves the relaying of block headers. Reviewing the remaining code that handles the aforementioned relaying of block headers did not surface any issues.