Added support for OpFlex domains.

This adds domains to the scoping of OpFlex servers and
messages.

This patch also moves the OpFlex-specific messages to
their own package, and adds fixes for using concrete
typing for Futures.

Change-Id: I67a9cfeebb5d40490cfa02780cf7c9b3d2acfb74
Signed-off-by: Thomas Bachman <tbachman@yahoo.com>