Changes to framework usage:

Changes to framework usage:

    * rather than subclass instantiation, xapps now use initialization and registration functions to register handlers
    * rmr xapps can now register handlers for specific message types (and they must prodive a default callback); if the user does this then "message to function routing" is now handled by the framework itself
    * RMRXapp now runs the polling loop in a thread, and returns execution back to the caller. The user is then free to loop, or do nothing, and call stop() when they want.
    * Raises tox coverage minimum to 70 from 50 (currently at 86)

Issue-ID: RIC-228
Change-Id: I15bfb708dbd14a46dc1207296e77383642d22b29
Signed-off-by: Tommy Carpenter <tc677g@att.com>