Please show arrival times in fork details

[murchandamus]

Since timestamps of blocks are usually off by dozens of seconds, it is generally interesting to also see arrival times of blocks. E.g., I was investigating a recent fork, and according to the arrival times on mempool•space, one block was seen 10 seconds before its timestamp, while the other was seen 14 seconds after its timestamp, so the timestamps would have had you believe there was a 24s gap between the two blocks, but mempool•space saw them within one second from each other. Anyway, it would be cool, if you showed the arrival times of fork blocks for your nodes on the chart!

[0xB10C]

Yes, I think that's a good idea. Once we have support for #109, we can store the arrival time in the database and expose it via the API and frontend.