Refactor to use GroupId class to wrap the byte array

Helps distinguish between group v1 and v2 ids

src/main/java/org/asamk/signal/manager/GroupIdV2.java

@@ -0,0 +1,14 @@
+package org.asamk.signal.manager;
+
+import java.util.Base64;
+
+public class GroupIdV2 extends GroupId {
+
+    public static GroupIdV2 fromBase64(String groupId) {
+        return new GroupIdV2(Base64.getDecoder().decode(groupId));
+    }
+
+    public GroupIdV2(final byte[] id) {
+        super(id);
+    }
+}