Build refactoring for eXo Software Factory compliance + cleanup

Maven clean up : 
* add dependency management, 
* remove all versions from children modules, 
* remove unused maven configurations, 
* POM.xml formatting

Maven change : 
* change groupId : org.benjp => org.exoplatform.addons.chat
* change artifactId : chat => chat-extension
* version change : 0.7-SNAPSHOT => 0.7.0-SNAPSHOT
* use the standard eXo Addons parent pom (org.exoplatform.addons:addons-parent-pom)

Remove all jars from the WEB-INF/lib directory

Remove spring.xml files which are useless (we use guava for juzu)