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.
earliest
There is no wallet activity before this date in epoch seconds. Pass null if you don't know.