pom.xml: Bumped version to 3.1.0-SNAPSHOT

JobDao.java: Added support for send_on_complete and remaining_retries columns.

Job.java: Added support for send_on_complete and remaining_retries columns.
FileUtil.java: Cleaned up documentation.

Job.java: Added property accessors for send_on_complete column.

Exam.java: Added constants for exam statues.

ConfigurationDao.java: Cleaned up documentation.
JobDao.java:
     * Added findRetryableJobs method to find retryable jobs
     * Added retryJob method to retry jobs