Now we store for each purchase in the tx_pool quantity and add up
to the total sum of items to buy. If purchase that is coming to the pool
wants to get more items than it is in the db + items from other purchases,
it is rejected right away.
Now, we store in meta of tx if tx is safex tx. After 1 hour,
safex tx will be checked if it's logic still stays correct. If not,
it is removed from the pool.