Add system wide management of core settings

bug:3505060

Since we want to have some settings that are used very frequently
by many applications (long-press timeout is one example) these should
be managed efficiently to reduce lookups from different processes
because in the case of a cache miss a disk I/O is performed. Now
the system manages such core settings and propagates them to the
application processes.

Change-Id: Ie793211baf8770f2181ac8ba9d7c2609dfaa32a7