Improve low memory dropbox reporting.

The msg is now constructed to try to bin these reports in
interesting ways.  We'll see.  Also change the tag name from
watchdog to lowmem, since sharkey is kindly taking care of
the back-end to handle this.

Improve how we put processes into low memory states to better
poke things like home and the previous app.

Also clean up some debug output, and add a few new am comment
options for controlling the current debug app.

Change-Id: I562a931a95244a2727bb7a6e1fd80dec259cdae2