QLowEnergyController - service discovery (OS X and iOS)

The initial version of service discovery failed to discover included services
correctly, actually this discovery requires some kind of 'graph traversal'
on the services tree. This patch re-implements the service discovery, discovering
included services also and avoiding ... loops in services referencing each other
(if it ever happens :) )

Change-Id: I60c6122fa5ddb922c21c99dd12024879cffad334
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>