moved application exception class to sch-pek-util

* renamed PekEJBException -> PekException
* repurposed message key in PekErrorCode to be a short message for the error
separated successful and unsuccessful response objects

* shared ancestor with isSuccess getter
* using PekErrorCode for errors
* custom serializer for PekErrorCode to include code and short message
api endpoint base class

for ensuring accept and content-type headers (application/json only)
removed unecessary javadoc and jboss-app.xml