Add support for new view type "x-html-sanitized"

[louiscryan]

Reviewers: shindig-dev,



Please review this at http://codereview.appspot.com/22049

Affected files:
  
../trunk/java/gadgets/src/main/java/org/apache/shindig/gadgets/DefaultUrlGenerator.java
  
../trunk/java/gadgets/src/main/java/org/apache/shindig/gadgets/render/SanitizedRenderingContentRewriter.java
  
../trunk/java/gadgets/src/main/java/org/apache/shindig/gadgets/servlet/JsonRpcHandler.java
  ../trunk/java/gadgets/src/main/java/org/apache/shindig/gadgets/spec/View.java
  
../trunk/java/gadgets/src/test/java/org/apache/shindig/gadgets/render/SanitizedRenderingContentRewriterTest.java
  
../trunk/java/gadgets/src/test/java/org/apache/shindig/gadgets/spec/ViewTest.java