Create SoundTriggerSession and associated collection within common

This patch creates a SoundTriggerSession and associated collection within
common policy pillar elements.
It moves the code from managerdefault and creates helpers function within
the collection.

Change-Id: I83ea230573c05e8ab99f4489c20059ed27678221
Signed-off-by: François Gaffie <francois.gaffie@intel.com>