Extract util methods to separate classes

src/main/java/org/asamk/signal/util/Hex.java

@@ -6,6 +6,9 @@ public class Hex {
             '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'
     };
 
+    private Hex() {
+    }
+
     public static String toStringCondensed(byte[] bytes) {
         StringBuffer buf = new StringBuffer();
         for (int i = 0; i < bytes.length; i++) {