Facebook is getting into real estate. This week, the company proposed building 1,500 apartments near its campus in Menlo Park, California, 15 percent of which it would set aside for low-income families. Urban planners and local developers call it a generous gesture that could bring sorely needed housing to the area. Facebook isn’t being totally altruistic here. The company plans to hire 6,500 employees within the next few years. To accommodate them, it wants to…