Conduit / Block Processor: Automatic Catchpoint Label Fetching

[winder]

Problem

The user must lookup the the current round, and map it to the correct catchpoint label. This process is tedious and a mistake could be made.

Solution

Add a new flag, or special catchpoint label (i.e. --catchpoint -). During startup, if requested, lookup the catchpoint label automatically.

1. Download the consolidated catchpoint file for the network in the genesis file: (i.e. for mainnet)
2. Find the largest catchpoint without going beyond the current round.
3. Attempt to initialize the ledger.