Add serialVersionUID to all exceptions

For more info, see [1].

[1]: https://stackoverflow.com/questions/146715/use-the-serialversionuid-or-suppress-warnings

app/src/androidTest/java/de/test/antennapod/util/service/download/NanoHTTPD.java

@@ -776,6 +776,7 @@ public abstract class NanoHTTPD {
     }
 
     public static final class ResponseException extends Exception {
+        private static final long serialVersionUID = 1L;
 
         private final Response.Status status;
 

core/src/main/java/de/danoeh/antennapod/core/gpoddernet/GpodnetServiceAuthenticationException.java

@@ -1,6 +1,7 @@
 package de.danoeh.antennapod.core.gpoddernet;
 
 public class GpodnetServiceAuthenticationException extends GpodnetServiceException {
+    private static final long serialVersionUID = 1L;
 
     public GpodnetServiceAuthenticationException() {
         super();

core/src/main/java/de/danoeh/antennapod/core/gpoddernet/GpodnetServiceBadStatusCodeException.java

@@ -1,6 +1,8 @@
 package de.danoeh.antennapod.core.gpoddernet;
 
 class GpodnetServiceBadStatusCodeException extends GpodnetServiceException {
+    private static final long serialVersionUID = 1L;
+
     private final int statusCode;
 
     public GpodnetServiceBadStatusCodeException(String message, int statusCode) {

core/src/main/java/de/danoeh/antennapod/core/gpoddernet/GpodnetServiceException.java

@@ -1,6 +1,7 @@
 package de.danoeh.antennapod.core.gpoddernet;
 
 public class GpodnetServiceException extends Exception {
+    private static final long serialVersionUID = 1L;
 
     GpodnetServiceException() {
     }

core/src/main/java/de/danoeh/antennapod/core/storage/DownloadRequestException.java

@@ -5,6 +5,7 @@ package de.danoeh.antennapod.core.storage;
  * or something went wrong while processing the request.
  */
 public class DownloadRequestException extends Exception {
+    private static final long serialVersionUID = 1L;
 
     public DownloadRequestException() {
         super();

core/src/main/java/de/danoeh/antennapod/core/util/InvalidFeedException.java

@@ -4,6 +4,7 @@ package de.danoeh.antennapod.core.util;
  * Thrown if a feed has invalid attribute values.
  */
 public class InvalidFeedException extends Exception {
+    private static final long serialVersionUID = 1L;
 
     public InvalidFeedException() {
     }

core/src/main/java/de/danoeh/antennapod/core/util/id3reader/ID3ReaderException.java

@@ -1,6 +1,7 @@
 package de.danoeh.antennapod.core.util.id3reader;
 
 public class ID3ReaderException extends Exception {
+    private static final long serialVersionUID = 1L;
 
     public ID3ReaderException() {
     }

core/src/main/java/de/danoeh/antennapod/core/util/vorbiscommentreader/VorbisCommentReaderException.java

@@ -1,6 +1,7 @@
 package de.danoeh.antennapod.core.util.vorbiscommentreader;
 
 public class VorbisCommentReaderException extends Exception {
+    private static final long serialVersionUID = 1L;
 
     public VorbisCommentReaderException() {
         super();