move configuration constants into separate class and make public

[cvaliente]

I moved the configuration constants into their own class. There were some duplicates (e.g.MASTER_ADDRESSES_KEY in both Input and Output). I also made them public so other applications can access them (e.g. a Hive SerDe can now use those Strings instead of redefining the same configuration parameters again)

also added new Integer DEFAULT_BUFFER_ROW_COUNT_KEY to replace hardcoded int in the application code.