[enh] do not require "currency" parameter for initial sync, even with WS2P

app/modules/crawler/index.ts

app/modules/crawler/lib/sync/ChunkGetter.ts

app/modules/crawler/lib/sync/P2PSyncDownloader.ts

app/modules/crawler/lib/sync/RemoteSynchronizer.ts

app/modules/ws2p/lib/WS2PConnection.ts

test/integration/misc/cli.ts

test/integration/tools/toolbox.ts

test/integration/ws2p/ws2p_connection.ts

test/integration/ws2p/ws2p_sync.ts