* config: add remoteControl/gRPC/timeInNanoSeconds
* grpc: consult with remoteControl/gRPC/timeInNanoSeconds whether timestamps should be in seconds or nanos
* engine: test if RPCServer.unixTimestamp() respects config/remoteControl/gRPC/timeInNanoSeconds
* engine: implement TestRPCServer_GetTicker_LastUpdatedNanos that makes sure TickerResponse.LastUpdated is returned in nanoseconds if configured
* config_example.json: add remoteControl/gRPC/timeInNanoSeconds
* engine: (1) test RPCServer.unixTimestamp() in parallel, (2) increase time tolerance of TestRPCServer_GetTicker_LastUpdatedNanos()
* engine: TestRPCServer_GetTicker_LastUpdatedNanos() now fetches a mock-up ticker to check timestamps