Fix x-axis values in tari-explorer

[Cifko]

In the tari-explorer we show a graph for Block times and the x-axis shows 1..25, but this is probably last n blocks, so it should show the actual tip..tip-25 (or reversed, I'm not sure about the order the data is shown) but if I'm not mistaken it's last 25 blocks.
The same for hash rates graph.