Return the name of the main activity

            :rtype: string

def get_main_activity(self):
        """
            Return the name of the main activity

            :rtype: string
        """
        x = set()
        y = set()

        for i in self.xml:
            activities_and_aliases = self.xml[i].getElementsByTagName("activity") + \
                                     self.xml[i].getElementsByTagName("activity-alias")

            for item in activities_and_aliases:
                # Some applications have more than one MAIN activity.
                # For example: paid and free content
                activityEnabled = item.getAttributeNS(NS_ANDROID_URI, "enabled")
                if activityEnabled is not None and activityEnabled != "" and activityEnabled == "false":
                    continue

                for sitem in item.getElementsByTagName("action"):
                    val = sitem.getAttributeNS(NS_ANDROID_URI, "name")
                    if val == "android.intent.action.MAIN":
                        x.add(item.getAttributeNS(NS_ANDROID_URI, "name"))

                for sitem in item.getElementsByTagName("category"):
                    val = sitem.getAttributeNS(NS_ANDROID_URI, "name")
                    if val == "android.intent.category.LAUNCHER":
                        y.add(item.getAttributeNS(NS_ANDROID_URI, "name"))

        z = x.intersection(y)
        if len(z) > 0:
            return self.format_value(z.pop())
        return None