Make proc stats UI app-centric instead of process-centric.

The UI now shows a much simpler overview of memory use for
the current measured duration, computing the weighted RAM
user per application.  (This is done basically by rolling up
each individual process into an app that can contain multiple
processes, and using the recently introduced weighted RAM for
all data processing.)

The details screen is updated to reflect this new design,
showing an overview of a particular application, which
separate entries for each process running for that app.

Change-Id: I47d79c30086d733eb37440a6c21b18a92b767d01