Returns:
            the name of the main activity

def main_activity(self):
        """
        Returns:
            the name of the main activity
        """
        x = set()
        y = set()
        for item in self._dom.getElementsByTagName("activity"):
            for sitem in item.getElementsByTagName("action"):
                val = sitem.getAttribute("android:name")
                if val == "android.intent.action.MAIN":
                    x.add(item.getAttribute("android:name"))
            for sitem in item.getElementsByTagName("category"):
                val = sitem.getAttribute("android:name")
                if val == "android.intent.category.LAUNCHER":
                    y.add(item.getAttribute("android:name"))
        z = x.intersection(y)
        if len(z) > 0:
            return z.pop()
        return None