Spark Java Article BAEL-498 (#912)

* Initial Commit for Spark Java Article BAEL-498

* reverting main pom.xml and rollbacking accidental changes.

* Changes as per review:

1. Added UserService
2. Renamed UserStore to UserServiceMapImpl
3. Removed Empty spaces in User.java
4. Removed AppTest
5. Changes in SparkRestExample for using UserServiceMapImp instead of
UserStore static functions.

* Suggested changes in print messages.

* Changes as per comments on github... for PR:
https://github.com/eugenp/tutorials/pull/912

* Changes in editUser function as per guidance by Kevin.

* Clean up

* added 1.8 config for pom.xml

* Clean up.

* Removed junit dep.

* Added Application/json in response type.

spark-java/src/main/java/com/baeldung/sparkjava/UserException.java

@@ -0,0 +1,13 @@
+package com.baeldung.sparkjava;
+
+public class UserException extends Exception{
+    
+    public UserException() {
+        super();
+    }
+    
+    public UserException(String message) {
+        super(message);
+    }
+
+}