Send HTTP status codes with GadgetException throws (issue207060)

[jo...@gmail.com]

Reviewers: shindig.remailer_gmail.com,

Description:
This CL does change the status codes that will be emitted to the direct
Shindig client.

General guideline:
* SC_BAD_REQUEST used when inputs are bad ie. query parameters or data
provided by the gadget developer.
* SC_BAD_GATEWAY used when data format (eg. FeedProcessor) is incorrect.

The line is fuzzy, so I'm interested in input.

Please review this at http://codereview.appspot.com/207060/show

Affected files:
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/AbstractSpecFactory.java
   java/gadgets/src/main/java/org/apache/shindig/gadgets/FeedProcessor.java
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/http/DefaultRequestPipeline.java
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/oauth/OAuthArguments.java
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/parse/caja/CajaCssLexerParser.java
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/parse/caja/CajaCssParser.java
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/parse/caja/CajaHtmlParser.java
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/servlet/HtmlAccelServlet.java
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/servlet/MakeRequestHandler.java
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/servlet/ProxyBase.java
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/servlet/ProxyHandler.java
    
java/gadgets/src/main/java/org/apache/shindig/gadgets/templates/TemplateLibraryFactory.java