Add udp support for loggly output

I added UDP support for Loggly. Initially I submitted this PR when the additional plugins were part of the core logstash repo. Initially Loggly support was added to the syslog output to minimize code duplication however it was then suggested that I move it to the Loggly output in order to make it a self contained output for Loggly.

Please let me know if you have any questions.