The Montgomery Healthcare System of Norristown including the hospital on Powell Street has officially become part of the Albert Einstein Healthcare Network.   Einstein is building a new state-of-the-art medical center on Germantown Pike in East Norriton that will open next year.   It will measure 360,000 square feet and have beds for 180 patients.   Einstein officials say it will give Montgomery County residents access to healthcare services that currently are only available at hospitals in Philadelphia.