Add RGBA to native picture type enum

Author: caprica

src/main/java/uk/co/caprica/vlcj/media/PictureType.java

@@ -30,7 +30,8 @@ public enum PictureType {
     ARGB(0),
     PNG (1),
     JPG (2),
-    WEBP(3);
+    WEBP(3),
+    RGBA(4);
 
     private static final Map<Integer, PictureType> INT_MAP = new HashMap<Integer, PictureType>();