Refactoring to imrove per-task transaction isolation.

This fixes existing bugs that cause duplicates when tasks die or are killed:
- Each executeBatch in a task is currently committed individually
- Currnetly the connection is implicitly committed during VerticaOutputFormat.close() which occurs during task kill

The fix includes:
- Setting autoCommit to false
- Handling commits and rollback in a new VerticaTaskOutputCommitter
- Adding ability to plug in a custom committer via mapred.vertica.output.committer. We plan to extend VerticaTaskOutputCommitter to implement custom table verification (and potentially manual rollback) in commitJob.
Adding license headers and addressing comments from github
Removing dated javadocs
Merge branch 'output_committer' of https://github.com/billonahill/Vertica-Hadoop-Connector

Conflicts:
	hadoop-connector/com/vertica/hadoop/VerticaConfiguration.java