Make the GUI aware of the new Subordinate info.

After a recent change in juju-core, the subordinate
info is available through the mega-watcher for
services and units. This branch enables the GUI to
fully support this where possible.

Also fixed the code so that uses of "subordinate" vs
"is_subordinate" are consistent.
Because this maps fields in the juju-core stream (capitalized) to internal JS model fields.