Add client::notification.bigImageUrl extra

closes #185

app/src/main/java/com/github/gotify/picasso/PicassoHandler.java

@@ -56,16 +56,18 @@ public class PicassoHandler {
                 .build();
     }
 
+    public Bitmap getImageFromUrl(String url) throws IOException {
+        return picasso.load(url).get();
+    }
+
     public Bitmap getIcon(Long appId) {
         if (appId == -1) {
             return BitmapFactory.decodeResource(context.getResources(), R.drawable.gotify);
         }
 
         try {
-            return picasso.load(
-                            Utils.resolveAbsoluteUrl(
-                                    settings.url() + "/", appIdToAppImage.get(appId)))
-                    .get();
+            return getImageFromUrl(
+                    Utils.resolveAbsoluteUrl(settings.url() + "/", appIdToAppImage.get(appId)));
         } catch (IOException e) {
             Log.e("Could not load image for notification", e);
         }

app/src/main/java/com/github/gotify/service/WebSocketService.java

@@ -314,6 +314,19 @@ public class WebSocketService extends Service {
         b.setContentText(message);
         b.setStyle(new NotificationCompat.BigTextStyle().bigText(formattedMessage));
 
+        String notificationImageUrl =
+                Extras.getNestedValue(String.class, extras, "client::notification", "bigImageUrl");
+
+        if (notificationImageUrl != null) {
+            try {
+                b.setStyle(
+                        new NotificationCompat.BigPictureStyle()
+                                .bigPicture(picassoHandler.getImageFromUrl(notificationImageUrl)));
+            } catch (Exception e) {
+                Log.e("Error loading bigImageUrl", e);
+            }
+        }
+
         NotificationManager notificationManager =
                 (NotificationManager) this.getSystemService(Context.NOTIFICATION_SERVICE);
         notificationManager.notify(Utils.longToInt(id), b.build());