Use server VAPID keys

mastodon/src/main/java/org/joinmastodon/android/api/session/AccountSessionManager.java

@@ -133,7 +133,7 @@ public class AccountSessionManager{
 					context,
 					session.getID(),
 					null,
-					null
+					session.app.vapidKey.replaceAll("=","")
 			);
 		} else if(PushSubscriptionManager.arePushNotificationsAvailable()){
 			session.getPushSubscriptionManager().registerAccountForPush(null);

mastodon/src/main/java/org/joinmastodon/android/utils/UnifiedPushHelper.java

@@ -33,7 +33,7 @@ public class UnifiedPushHelper {
 					context,
 					accountSession.getID(),
 					null,
-					null
+					accountSession.app.vapidKey.replaceAll("=","")
 			);
 		}
 	}