Added form request (application/x-www-form-urlencoded) support for sparql end point; refactored the rest api codes for sparql.

https://www.pivotaltracker.com/s/projects/684825/stories/72619228

We should be able to submit sparql with form request (application/x-www-form-urlencoded) now.  The original support for contentTypeSPARQLQuery is changed to the default content type since I see the sparql integration tests depend on it. 
I made the form request to accept any parameters for the sparql at this time if there are only have one parameter in the form, but assume parameter "query" is the required parameter for the sparql and raise a error to prompt for it if the query is not found. Please let me know if you have other thoughts.
Use: http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Strings.html#isNullOrEmpty(java.lang.String)