Check whether prices were posted in the current block before posting more

[haydenshively]

[Solidity]

Posting prices requires anywhere from 400k to 700k gas. If someone has already posted prices in the current block, it indicates that we have most likely lost a bidding war. Rather than blindly trying to post prices again, we should check the timestamp and only post prices if nobody else has.

This should save us a lot of money on lost bids. Like probably $30 -> $0.30