Merge TCP Speed Task

I include the new TCP Speed Task (measuring TCP Throughput) in the MobiPerf, and it runs against the nearest M-Lab slices. Uplink and downlink task are measuring the network throughput status in both directions. To reduce the memory requirement, we reduce the size of the splashscreen image to limit the occurance of out-of-memory failure.

Detail of the throughput task is shared through Google Docs with title "MobiPerf Throughput Test Summary".