BUG-625: migrate FlowProgrammerAdapter

This migrates FlowProgrammerAdapter from xtend to pure Java, cleaning it
up in the process. A bunch of possible omissions/errors are marked with
FIXME for someone to follow up.

Change-Id: I057449bd7a569a75e30182493727dbc200f83e62
Signed-off-by: Robert Varga <rovarga@cisco.com>