Intermediary with LND running in Neutrino mode

[adambor]

Currently a bitcoin full node is required to run the intermediary node (mainly due to LND) - this means downloading the whole bitcoin blockchain with txindex -> resulting in 1TB of disk space and long syncing time.

LND supports light client mode (Neutrino), which could be used to sync the node fast.

Open questions:

• does Neutrino mode allow LND's getBlock call which would allow us to compute a merkle proof of the transaction inclusion

Todo:

• run LND in neutrino mode and check that required API calls work (getChainTransaction, getBlock, getBlockHeader, getWalletInfo)
• write a bitcoin RPC implementation purely using LND's gRPC API