AGREEMENT AND PLAN OF MERGER BY AND AMONG QUALITY CARE PROPERTIES, INC., QCP AL REIT, LLC, QCP SNF WEST REIT, LLC, QCP SNF CENTRAL REIT, LLC, QCP SNF EAST REIT, LLC, QCP HOLDCO REIT, LLC, QCP TRS, LLC, WELLTOWER INC. AND POTOMAC ACQUISITION LLC APRIL...