Use Jackson XML package for JSON result generation.

Seems to be the only JSON generator with streaming support.
diff --git a/asterix-app/pom.xml b/asterix-app/pom.xml
index 48c4ee5..b47fec1 100644
--- a/asterix-app/pom.xml
+++ b/asterix-app/pom.xml
@@ -208,17 +208,22 @@
 			<type>jar</type>
 			<scope>test</scope>
 		</dependency>
-                <dependency>
-                    <groupId>net.sourceforge.cobertura</groupId>
-                    <artifactId>cobertura</artifactId>
-                    <version>1.9.4</version>
-                </dependency>
-                <dependency>
-                	<groupId>edu.uci.ics.asterix</groupId>
-                	<artifactId>asterix-test-framework</artifactId>
-                	<version>0.0.5-SNAPSHOT</version>
-                	<scope>test</scope>
-                </dependency>
+        <dependency>
+            <groupId>net.sourceforge.cobertura</groupId>
+            <artifactId>cobertura</artifactId>
+            <version>1.9.4</version>
+        </dependency>
+        <dependency>
+            <groupId>edu.uci.ics.asterix</groupId>
+            <artifactId>asterix-test-framework</artifactId>
+            <version>0.0.5-SNAPSHOT</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-core</artifactId>
+            <version>2.2.0</version>
+        </dependency>
 	</dependencies>
 
 </project>