Change deadline from block number to timestamp

[matt-user]

Motivation

Important: It would be cool if we could hold of on implementing this change until #290 is merged bc it would break part of the english auction ui frontend

Description

Change the auction deadline to be a timestamp instead of a block number.

Motivation

As we do not know current block times it it hard to use a block number as a deadline bc we do not actually know how quickly the deadline will be reached.