First pass at adding the cache quota suggestions.

This currently integrates with installd, but not with
any framework API to expose this information to apps.

The first pass, as per the design doc, adds a service
which polls for large changes in the file system free space.
If enough spaces changes, it begins a recalculation of the
cache quotas and pipes the information down to installd.
This calculation is done in the updateable ExtServices.

Further enhancements in later patches include integrating this
to listen to package install and removal events, caching the
last computed quota values into an XML file on disk to load
on boot, and exposing the information to apps.

Bug: 33965858
Test: ExtServices unit test

Change-Id: Ie39f228b73532cb6ce2f98529f7c5df0839202ae