start
Start syncing against the blockchain provided with @ref usesChain, which MUST be called first. (or call @ref addBlockchain do do both). You should determine either earliestHeight or earliestDate, possibly via Rostrum, or you may be in for a very long sync operation.
Parameters
earliest
There is no wallet activity before this block height. Pass null if you don't know (starts at 0), -1 for now.
earliest
There is no wallet activity before this date in epoch seconds. Pass null if you don't know (starts at 0), -1 for now.