Add Marvel version

If we want to be able to display Marvel version in Nodes info, we need to add it in `es-plugin.properties` file.

Closes #155.

agent/pom.xml

@@ -74,6 +74,12 @@
     </dependencies>
 
     <build>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
         <plugins>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>

agent/src/main/resources/es-plugin.properties

@@ -1 +1,2 @@
-plugin=org.elasticsearch.marvel.agent.Plugin
+plugin=org.elasticsearch.marvel.agent.Plugin
+version=${project.version}