reverse-string: add to track (#1126)

* reverse-string: add to track

* reverse-string: improve example.py

* reverse-string: update config.json

* reverse-string: add uuid

* reverse-string: rename test file

exercises/reverse-string/example.py

@@ -0,0 +1,2 @@
+def reverse(input=''):
+    return input[::-1]