Added default serialVersionUID for new Exception classes

https://github.com/stefan-niedermann/nextcloud-deck/issues/208

src/main/java/com/nextcloud/client/integration/AppCannotHandleNotificationException.java

@@ -21,4 +21,5 @@
 package com.nextcloud.client.integration;
 
 public class AppCannotHandleNotificationException extends Exception {
+    private static final long serialVersionUID = 1L;
 }

src/main/java/com/nextcloud/client/integration/AppNotInstalledException.java

@@ -21,4 +21,5 @@
 package com.nextcloud.client.integration;
 
 public class AppNotInstalledException extends Exception {
+    private static final long serialVersionUID = 1L;
 }