Resolve fiat prices and values for orders

• Support fiat prices and values for ETH- and BTC- orders in the Orders page (open orders)
• Support hypothetical fiat prices and values for ETH- and BTC orders in the Orders page (closed orders)
• Support open orders (est. USD) and market history (hyp. USD) in Market page
• Format prices < $1 to 6dp (vs 2dp)
• Minor Optimizations
  • Price polling delayed to 20s vs 5
  • ETH price sync now on relevant pages only