FANWOOD — The borough council on Tuesday agreed to a mediation agreement relating to its affordablehousing obligations. Fair Share Housing Center, the advocacy group behind the push for more affordable housing in the state, filed a challenge against Fanwood’s affordable housing plan said Diane Dabulis, the borough’s affordable housing attorney. She told the council that Fair Share Housing has challenged “practically every community” in the state and said Fanwood’s agreement will mean an increase in the setaside for affordable units from 15 percent to 20 percent.