Smarter data fetching for the dashboard

[whoabuddy]

Two quick improvements in the dashboard functions could be:

For mining data, when the current block changes:

• right now it blindly fetches 5 blocks worth of mining data
• check block numbers in array before fetching new data
• possible pattern: see if any are still valid and keep, then fetch new
  • scenario 1: normal flow (block + 1)
  • scenario 2: old data in range (block + 3)
  • scenario 3: way stale block data (block + 50)

For stacking data:

• right now it fetches new data if block height changes
• instead it should fetch data if current reward cycle changes
• could use same patterns as mining above, but updated less often anyway so may not be worth the complexity