Add the openSocial namespace to entries from the activity stream produced by Shindig (issue4398045)

[rbaxter85]

Reviewers: woodser_us.ibm.com,

Description:
Part of the migration of some of the OpenSocial components to activity
streams involves namespacing some of the OpenSocial properties that do
not match to Activity Stream properties. This patch adds the openSocial
namespace to the activity streams implementation so we can begin to
build out these OpenSocial extensions.
Please review this at http://codereview.appspot.com/4398045/

Affected files:
  content/sampledata/canonicaldb.json
   
java/social-api/src/main/java/org/apache/shindig/social/core/model/ActivityEntryImpl.java
   
java/social-api/src/main/java/org/apache/shindig/social/core/model/OpenSocialImpl.java
   
java/social-api/src/main/java/org/apache/shindig/social/core/util/xstream/XStream081Configuration.java
   
java/social-api/src/main/java/org/apache/shindig/social/opensocial/model/ActivityEntry.java
   
java/social-api/src/main/java/org/apache/shindig/social/opensocial/model/OpenSocial.java
   
java/social-api/src/test/java/org/apache/shindig/social/dataservice/integration/fixtures/ActivityEntryJsonGroup.json
   
java/social-api/src/test/java/org/apache/shindig/social/dataservice/integration/fixtures/ActivityEntryJsonId.json
   
java/social-api/src/test/java/org/apache/shindig/social/dataservice/integration/fixtures/ActivityEntryJsonIds.json
   
java/social-api/src/test/java/org/apache/shindig/social/dataservice/integration/fixtures/ActivityEntryJsonUpdated.json