The Mequon Common Council has adopted a 30-year master plan to transform its quiet civic campus into a vibrant community hub known as Mequon Commons.After more than a year of work, the city approved the master plan this month. It is estimated to cost more than $20 million over a decade of work. The centerpiece of the campus will be a new plaza and amphitheater, along with an updated playground and pool.The first of three phases will focus on rem…