Work on more low memory reporting to apps.

There are now some new trim memory levels that are sent to
non-background applications as RAM becomes low.

There is a new API for an application to retrieve information
about memory trimming and such on demand.

Fixed various checks against the memory trim level to be
robust (not compare against exact values).

Change-Id: Ifd1c6151124350168aef20a94e517166fd2e03eb