Work on issue #62065889: Assess thresholds and criteria for killing...

...background processes (CPU, etc)

Add full configuration params for adjusting these settings (some were
already there).

Also...  as long as we are doing this...

- Get rid of all of the wakelock stuff.  That is completely pointless
now that we aren't even allowing cached processes to hold wake locks.

- This greatly simplifies the code, since we don't need to deal with
two different policies for how we do checks.  Instead, we just regularly
check for CPU and the CPU check interval.

- And make the CPU check more aggressive and have much more flexibility
for tuning: there are now 4 different maximum CPU use levels, depending
on how long the process has been in the cached state.  This allows us to
be more strict on CPU use the longer it is sitting in the background.

Note that CPU use tracking only happens while the device is not
plugged in to power...  I'll leave this for now, but I think in the
future we should think about applying these limits even when plugged
in, because in either case cached apps should really not be doing
much.

Test: manual
Change-Id: I68f4ab68be5f7d5fc4822005107fb60ef07a374d