Allow injection of new features directories/resources via multibindings (issue1197041)

[lindner]

Reviewers: shindig.remailer_gmail.com,


Please review this at http://codereview.appspot.com/1197041/show

Affected files:
  M  
java/gadgets/src/main/java/org/apache/shindig/gadgets/DefaultGuiceModule.java
  M  
java/gadgets/src/main/java/org/apache/shindig/gadgets/features/FeatureRegistry.java
  M  
java/gadgets/src/test/java/org/apache/shindig/gadgets/features/FeatureRegistryTest.java
  M  
java/gadgets/src/test/java/org/apache/shindig/gadgets/templates/tags/TemplateBasedTagHandlerTest.java