[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[uapp][psutils] Add the 'memgraph' tool to dump task/vmo JSON

Dumps everything that 'ps --json' did, plus all of the VMOs reachable
from user processes.

This emits all of the information necessary to draw a VMO reference and
clone graph for all of userspace.

For MG-721: "Add a way to track non-mapped VMO memory usage"

Change-Id: I2ff12eec0a27053c94a5f87e9a32682c76f1fbb0

[uapp] Make 'ps --json' dump kernel memory info

Also splits out a helper function to get the root resource.

MG-819 #done

Change-Id: I29806da74289e2eb004391603af75fcdea5c68f0